opinion: Justice White
  delivered the opinion of the Court.
  Under Griggs v. Duke Power Co., 401 U. S. 424 (1971), a prima facie violation of Title VII of the Civil Rights Act of 1964, 78 Stat. 253, as amended, 42 U. S. C. §2000e et seq. (1976 ed. and Supp. IV), “may be established by policies or practices that are neutral on their face and in intent but that nonetheless discriminate in effect against a particular group.” Teamsters v. United States, 431 U. S. 324, 349 (1977). A seniority system “would seem to fall under the Griggs rationale” if it were not for § 703(h) of the Civil Rights Act. Ibid. That section, as set forth in 42 U. S. C. § 2000e-2(h), provides in pertinent part:
  “Notwithstanding any other provision of this sub-chapter, it shall not be an unlawful employment practice for an employer to apply different standards of compensation, or different terms, conditions, or privileges of employment pursuant to a bona fide seniority or merit system, . . . provided that such differences are not the result of an intention to discriminate because of race, color, religion, sex, or national origin, nor shall it be an unlawful employment practice for an employer to give and to act upon the results of any professionally developed ability test provided that such test, its administration or action upon the results is not designed, intended or used to discriminate because of race, color, religion, sex, or national origin. ...”
  Under § 703(h), the fact that a seniority system has a discriminatory impact is not alone sufficient to invalidate the system; actual intent to discriminate must be proved. The Court of Appeals in this case, however, held that § 703(h) does not apply to seniority systems adopted after the effective date of the Civil Rights Act. We granted the petition for certiorari to address the validity of this construction of the section. 452 U. S. 937 (1982).
  H-I
  Petitioner American Tobacco Co. operates two plants m Richmond, Va., one which manufactures cigarettes and one which manufactures pipe tobacco. Each plant is divided into a prefabrication department, which blends and prepares tobacco for further processing, and a fabrication department, which manufactures the final product. Petitioner Bakery, Confectionery & Tobacco Workers’ International Union and its affiliate Local 182 are the exclusive collective-bargaining agents for hourly paid production workers at both plants.
  It is uncontested that prior to 1963 the company and the union engaged in overt race discrimination. The union maintained two segregated locals, and black employees were assigned to jobs in the lower paying prefabrication departments. Higher paying jobs in the fabrication departments were largely reserved for white employees. An employee could transfer from one of the predominately black prefabrication departments to one of the predominately white fabrication departments only by forfeiting his seniority.
  In 1963, under pressure from Government procurement agencies enforcing the antidiscrimination obligations of Government contractors, the company abolished departmental seniority in favor of plantwide seniority and the black union local was merged into the white local. However, promotions were no longer based solely on seniority but rather on seniority plus certain qualifications, and employees lost accumulated seniority in the event of a transfer between plants. Between 1963 and 1968, when this promotions policy was in force, virtually all vacancies in the fabrication departments were filled by white employees due to the discretion vested in supervisors to determine who was qualified.
  In November 1968, the company proposed the establishment of nine lines of progression, six of which are at issue in this case. The union accepted and ratified the lines of progression in 1969. Each line of progression generally consisted of two jobs. An employee was not eligible for the top job in the line until he had worked in a bottom job. Four of the six lines of progression at issue here consisted of nearly all-white top jobs from the fabrication departments linked with nearly all-white bottom jobs from the fabrication departments; the other two consisted of all-black top jobs from the prefabrication departments linked with all-black bottom jobs from the prefabrication departments. The top jobs in the white lines of progression were among the best paying jobs in the plants.
  On January 3, 1969, respondent Patterson and two other black employees filed charges with the Equal Employment Opportunity Commission alleging that petitioners had discriminated against them on the basis of race. The EEOC found reasonable cause to believe that petitioners’ seniority, wage, and job classification practices violated Title VII. After conciliation efforts failed, the employees filed a class action in District Court in 1973 charging petitioners with racial discrimination in violation of Title VII and 42 U. S. C. § 1981. Their suit was consolidated for trial with a subsequent Title VII action filed by the EEOC alleging both race and sex discrimination. Following trial, the District Court held that petitioners’ seniority, promotion, and job classification practices violated Title VII. The court found that six of the nine lines of progression were not justified by business necessity and “perpetuated past discrimination on the basis of sex and race.” App. 32. The court enjoined the company and the union from further use of the six lines of progression. The Court of Appeals for the Fourth Circuit affirmed and remanded for further proceedings with respect to remedy, Patterson v. American Tobacco Co., 535 F. 2d 257 (1976), and we denied a petition for certiorari. 429 U. S. 920 (1976).
  On remand petitioners moved to vacate the District Court’s 1974 orders and to dismiss the complaints on the basis of this Court’s decision in Teamsters v. United States, 431 U. S. 324 (1977), which held that § 703(h) insulates bona fide seniority systems from attack even though they may have discriminatory impact on minorities. The District Court denied the motions, holding that petitioners’ seniority system “is not a bona fide system under Teamsters . . . because this system operated right up to the day of trial in a discriminatory manner.” App. 110. A divided panel of the Court of Appeals agreed that “Teamsters requires no modification of the relief we approved with regard to . . . lines of progression . . . ,” because they were not part of a seniority system within the meaning of § 703(h). 586 F. 2d 300, 303 (1978).
  The Court of Appeals reheard the case en banc. It did not decide whether the lines of progression were part of a seniority system. Instead, it held that even if the lines of progression were considered part of a seniority system, “Congress intended the immunity accorded seniority systems by § 703(h) to run only to those systems in existence at the time of Title VIPs effective date, and of course to routine post-Act applications of such systems.” 634 F. 2d 744, 749 (1980). We reverse.
  II
  Petitioners argue that the plain language of § 703(h) applies to post-Act as well as pre-Act seniority systems. The respondent employees claim that the provision “provides a narrow exemption [from the ordinary discriminatory impact test] which was specifically designed to protect bona fide seniority systems which were in existence before the effective date of Title VII.” Brief for Respondent Patterson et al. 29. Respondent EEOC supports the judgment below, but urges us to interpret § 703(h) so as to protect the post-Act application of a bona fide seniority system but not the post-Act adoption of a seniority system or an aspect of a seniority system.
  As in all cases involving statutory construction, “our starting point must be the language employed by Congress,” Reiter v. Sonotone Corp., 442 U. S. 330, 337 (1979), and we assume “that the legislative purpose is expressed by the ordinary meaning of the words used.” Richards v. United States, 369 U. S. 1, 9 (1962). Thus “[a]bsent a clearly expressed legislative intention to the contrary, that language must ordinarily be regarded as conclusive.” Consumer Product Safety Comm’n v. GTE Sylvania, Inc., 447 U. S. 102, 108 (1980). The plain language of § 703(h) is particularly cogent in light of the circumstances of its drafting. It was part of the Dirksen-Mansfield compromise bill which represented “not merely weeks, but months of labor.” 110 Cong.Rec. 11935 (1964) (remarks of Sen. Dirksen). As Senator Dirksen explained: “I doubt very much whether in my whole legislative lifetime any measure has received so much meticulous attention. We have tried to be mindful of every word, of every comma, and of the shading of every phrase.” Ibid.
  On its face § 703(h) makes no distinction between pre- and post-Act seniority systems, just as it does not distinguish between pre- and post-Act merit systems or pre- and post-Act ability tests. The section does not take the form of a saving clause or a grandfather clause designed to exclude existing practices from the operation of a new rule. Other sections of Title VII enacted by the same Congress contain grandfather clauses, see § 701(b), 78 Stat. 253, as amended, 42 U. S. C. §2000e-(b), a difference which increases our reluctance to transform a provision that we have previously described as “defining what is and what is not an illegal discriminatory practice . . . ,” Franks v. Bowman Transportation Co., 424 U. S. 747, 761 (1976), from a definitional clause into a grandfather clause.
  The EEOC’s position, which is urged by Justice Brennan’s dissent, is no more supportable. In permitting an employer to “apply” different terms of employment pursuant to a seniority system, § 703(h) does not distinguish between seniority systems adopted before and those adopted after the effective date of the Act. That distinction would require reading § 703(h) as though the reference to a seniority system were followed by the words “adopted prior to the effective date of this section.” But the section contains no such limitation. To be cognizable, a claim that a seniority system has a discriminatory impact must be accompanied by proof of a discriminatory purpose.
  Furthermore, for the purpose of construing § 703(h), the proposed distinction between application and adoption on its face makes little sense. The adoption of a seniority system which has not been applied would not give rise to a cause of action. A discriminatory effect would arise only when the system is put into operation and the employer “applies” the system. Such application is not infirm under § 703(h) unless it is accompanied by a discriminatory purpose. An adequate remedy for adopting a discriminatory seniority system would very likely include an injunction against the future application of the system and backpay awards for those harmed by its application. Such an injunction, however, would lie only if the requirement of § 703(h) — that such application be intentionally discriminatory — were satisfied.
  Under the EEOC’s interpretation of the statute, plaintiffs who file a timely challenge to the adoption of a seniority system arguably would prevail in a Title VII action if they could prove that the system would have a discriminatory impact even if it was not purposefully discriminatory. Post, at 86. See Griggs v. Duke Power Co., 401 U. S. 424 (1971). On the other hand, employees who seek redress under Title VII more than 180 days after the adoption of a seniority system — for example, all persons whose employment begins more than 180 days after an employer adopts a seniority system — would have to prove the system was intentionally discriminatory. Yet employees who prevailed by showing that a bona fide seniority system had a discriminatory impact although not adopted with discriminatory intent would not be entitled to an injunction forbidding the application of the system: § 703(h) plainly allows the application of such a seniority system.
  A further result of the EEOC’s theory would be to discourage unions and employers from modifying pre-Act seniority systems or post-Act systems whose adoption was not timely challenged. Any modification, if timely challenged, would be subject to the Griggs standard — even if it benefited persons covered by Title VII — thereby creating an incentive to retain existing systems which enjoy the protection of § 703(h).
  Statutes should be interpreted to avoid untenable distinctions and unreasonable results whenever possible. The EEOC’s reading of § 703(h) would make it illegal to adopt, and in practice to apply, seniority systems that fall within the class of systems protected by the provision. We must, therefore, reject such a reading.
  Ill
  Although the plain language of § 703(h) makes no distinction between pre-Act and post-Act seniority systems, the court below found support for its distinction between the two in the legislative history. Such an intepretation misreads the legislative history.
  We have not been informed of and have not found a single statement anywhere in the legislative history saying that § 703(h) does not protect seniority systems adopted or modified after the effective date of Title VII. Nor does the legislative history reveal that Congress intended to distinguish between adoption and application of a bona fide seniority system. The most which can be said for the legislative history of § 703(h) is that it is inconclusive with respect to the issue presented in this case.
  As we have previously described, see Franks v. Bowman Transportation Co., 424 U. S., at 759-761, the initial bill passed by the House of Representatives on February 10, 1964, did not contain § 703(h) and neither the bill nor the majority Judiciary Committee Report even mentioned seniority. However, the House Minority Report warned that the bill, if enacted, would destroy seniority. H. R. Rep. No. 914, 88th Cong., 1st Sess., 64-65 (1963). Following a 17-day debate over whether the bill should be referred to committee, the Senate voted to reject the motion to refer it to committee and began to formally consider the merits of the bill on March 30, 1964. Meanwhile, a bipartisan group led by Senators Dirksen, Mansfield, Humphrey, and Kuchel worked to reach agreement on amendments to the House bill which would ensure its passage. Vaas, Title VII: Legislative History, 7 B. C. Ind. & Com. L. Rev. 431, 445 (1966). The Mansfield-Dirksen compromise, which contained § 703(h), was introduced on the Senate floor in the form of a substitute bill on May 26, 1964. Prior to the introduction of the Mansfield-Dirksen substitute, supporters of the House bill responded to charges that it would destroy existing seniority rights. On April 8, 1964, Senator Clark made a speech in which he stated that “it is clear that the bill would not affect seniority at all.” 110 Cong. Rec. 7207 (1964). In support of his conclusion, he inserted three documents into the Congressional Record which this Court has characterized as “authoritative indicators” of the purpose of § 703(h), Teamsters v. United States, 431 U. S., at 352, and which the court below relied upon for its conclusion that post-Act seniority systems were not intended to be protected by § 703(h). See 634 F. 2d, at 749-750, n. 5.
  The first document was a Justice Department memorandum which stated, in part, that “Title VII would have no effect on seniority rights existing at the time it takes effect.” The second document was an interpretive memorandum which had been prepared by Senator Clark and Senator Case, and it also said Title VII would “have no effect on established seniority rights.” Senator Clark also introduced written answers to questions propounded by Senator Dirksen which included the statement, “Seniority rights are in no way affected by the bill.”
  On the basis of the statements that Title VII would not affect “existing” and “established” seniority rights, respondents infer that Title VII would affect seniority rights which were not “established” or “existing” when the Act became effective. Such an inference is unjustified. While the materials which Senator Clark inserted into the Congressional Record did speak in terms of Title VII not affecting “vested,” “existing,” or “established” seniority rights, they did so because they were responding to a specific charge made by the bill’s opponents, namely, that the bill would destroy existing seniority rights. Had Senator Clark intended that the bill not protect post-Act seniority systems, it is highly unlikely he would have stated on the floor of the Senate that “the bill would not affect seniority at all,” 110 Cong. Rec. 7207 (1964), or introduced a written response to a question posed by Senator Dirksen which said:
  “Seniority rights are in no way affected by the bill. If under a ‘last hired, first fired’ agreement a Negro happens to be the “last hired,’ he can still be ‘first fired’ so long as it is done because of his status as ‘last hired’ and not because of his race.” Id., at 7217.
  Respondents’ argument also ignores numerous other references to seniority by proponents of Title VII which were couched in terms of “seniority” rather than “existing seniority rights.” See, e. g., id., at 5423 (remarks of Sen. Humphrey); id., at 6564 (remarks of Sen. Kuchel); id., at 6565-6566 (memorandum prepared by House Republican sponsors); id., at 11768 (remarks of Sen. McGovern). In addition, the few references to seniority after § 703(h) was added to the bill are to the effect that “the Senate substitute bill expressly protects valid seniority systems.” Id., at 14329 (letter from Sen. Dirksen to Sen. Williams). See also id., at 14331 (remarks of Sen. Williams).
  Going behind the plain language of a statute in search of a possibly contrary congressional intent is “a step to be taken cautiously” even under the best of circumstances. Piper v. Chris-Craft Industries, Inc., 430 U. S. 1, 26 (1977). “[I]n light of its unusual legislative history and the absence of the usual legislative materials,” Franks v. Bowman Construction Co., 424 U. S., at 761, we would in any event hesitate to give dispositive weight to the legislative history of § 703(h). More importantly, however, the history of § 703(h) does not support the far-reaching limitation on the terms of § 703(h) announced by the court below and urged by respondents. The fragments of legislative history cited by respondents, regardless of how liberally they are construed, do not amount to a clearly expressed legislative intent contrary to the plain language of the statute. Consumer Product Safety Comm’n v. GTE Sylvania, Inc., 447 U. S., at 108.
  > ) — I
  Our prior decisions have emphasized that “seniority systems are afforded special treatment under Title VII itself,” Trans World Airlines, Inc. v. Hardison, 432 U. S. 63, 81 (1977), and have refused to narrow § 703(h) by reading into it limitations not contained in the statutory language. In Teamsters v. United States, supra, we held that § 703(h) exempts from Title VII the disparate impact of a bona fide seniority system even if the differential treatment is the result of pre-Act racially discriminatory employment practices. Similarly, by holding that “[a] discriminatory act which is not made the basis for a timely charge is the legal equivalent of a discriminatory act which occurred before the statute was passed,” United Air Lines, Inc. v. Evans, 431 U. S. 553, 558 (1977), the Court interpreted § 703(h) to immunize seniority systems which perpetuate post-Act discrimination. Thus taken together, Teamsters and Evans stand for the proposition stated in Teamsters that “[s]ection 703(h) on its face immunizes all bona fide seniority systems, and does not distinguish between the perpetuation of pre- and post-Act” discriminatory impact. Teamsters, 431 U. S., at 348, n. 30 (emphasis added). Section 703(h) makes no distinction between seniority systems adopted before its effective date and those adopted after its effective date. Consistent with our prior decisions, we decline respondents' invitation to read such a distinction into the statute.
  Seniority provisions are of “overriding importance” in collective bargaining, Humphrey v. Moore, 375 U. S. 335, 346 (1964), and they “are universally included in these contracts.” Trans World, Airlines, Inc. v. Hardison, supra, at 79. See also Aaron, Reflections on the Legal Nature and Enforceability of Seniority Rights, 75 Harv. L. Rev. 1532, 1534 (1962). The collective-bargaining process “lies at the core of our national labor policy . . . .” Trans World Airlines, Inc. v. Hardison, supra, at 79. See, e. g., 29 U. S. C. § 151. Congress was well aware in 1964 that the overall purpose of Title VII, to eliminate discrimination in employment, inevitably would, on occasion, conflict with the policy favoring minimal supervision by courts and other governmental agencies over the substantive terms of collective-bargaining agreements. California Brewers Assn. v. Bryant, 444 U. S. 598, 608 (1980). Section 703(h) represents the balance Congress struck between the two policies, and it is not this Court’s function to upset that balance.
  Because a construction of § 703(h) limiting its application to seniority systems in place prior to the effective date of the statute would be contrary to its plain language, inconsistent with our prior cases, and would run counter to the national labor policy, we vacate the judgment below and remand for further proceedings consistent with this opinion.
  So ordered.
  . Title VII became effective July 2, 1965, one year after its enactment.
  The en banc court remanded the case to the District Court for additional proceedings to determine whether the plantwide seniority system in effect since 1963 is a bona fide seniority system within the contemplation of § 703(h). See 634 F. 2d, at 750. This issue is not before the Court.
  Prior to 1972, Title VII generally required charges to be filed within 90 days of an alleged discriminatory practice. Section 706(e), 78 Stat. 260, was amended in 1972. It now requires aggrieved persons to file a charge “within one hundred and eighty days after the alleged unlawful employment practice occurred . . . .” 42 U. S. C. §2000e-5(e).
  The facts of this case give rise to just such an anomaly under the EEOC theory. The respondent employees filed race discrimination charges within 90 days of the adoption of the lines of progression but sex discrimination charges were filed more than 90 days after the adoption. Under the EEOC theory, the lines of progression would be analyzed under two different tests: the Griggs impact test and the § 703(h) intentional discrimination test.
  "Significant freedom must be afforded employers and unions to create differing seniority systems.” California Brewers Assn. v. Bryant, 444 U. S. 598, 608 (1980). Respondents’ interpretation of § 703(h) would impinge on that freedom by discouraging modification of existing seniority systems or adoption of new systems.
  Justice Brennan’s dissent admits that the legislative history “does not contain any explicit reference to the distinction between adoption and application.” Post, at 83. Nor is there explicit basis for the proposition that § 703(h) applies only to those plans “adopted” prior to the effective date of the Act. It is nevertheless claimed that the legislative history supports reading this distinction into the statute. Post, at 83, n. 8. Had Congress intended so fundamental a distinction, it would have expressed that intent clearly in the statutory language or the legislative history. It did not do so, however, and it is not this Court’s function “to sit as a super-legislature,” Griswold v. Connecticut, 381 U. S. 479, 482 (1965), and create statutory distinctions where none were intended.
  H. R. 7152, 88th Cong., 1st Sess. (1963).
  H. R. Rep. No. 914, 88th Cong., 1st Sess. (1963).
  110 Cong. Rec. 11926 (1964).
  For examples of charges that the bill would destroy existing seniority rights see, e. g., H. R. Rep. No. 914, supra, at 64-66 (Minority Report); 110 Cong. Rec. 486-489 (1964) (remarks of Sen. Hill); id., at 11471 (remarks of Sen. Javits discussing charges made by Governor Wallace).
  Senator Humphrey, one of the drafters of the Mansfield-Dirksen substitute, explained that § 703(h) did not alter the meaning of Title VII but “merely clarifie[d] its present intent and effect.” Id., at 12723. Therefore statements made prior to the introduction of § 703(h) by proponents of Title VII are evidence of the meaning of § 703(h).
  Id., at 7207. The full text of the statement with respect to seniority may be found in Franks v. Bowman Transportation Co., 424 U. S. 747, 760, n. 16 (1976).
  110 Cong. Rec. 7213 (1964). The full text of the statement with respect to seniority may be found in Franks v. Bowman Transportation Co., supra, at 759, n. 15.
  110 Cong. Rec. 7217 (1964). The questions and answers with respect to seniority may be found in Franks v. Bowman Transportation Co., supra, at 760-761, n. 16.
  Strictly speaking, Senator Clark’s statement that Title VII would not affect seniority is incorrect. Title VII does affect seniority rights, for Franks v. Bowman Transportation Co., supra, allows awards of retroactive seniority to victims of unlawful discrimination. However, Senator Clark’s technical error does not alter our conclusion that he and other key proponents of the bill intended that it have minimal impact on seniority systems.
  Nowhere in Teamsters v. United States does the Court indicate when the seniority system at issue there was adopted, and examination of the record illustrates the difficulty of fixing an adoption date. Article V of the National Motor Freight Agreement of 1964 contains a seniority provision subject to modification by area agreements and local union riders. See Brief for Petitioner Teamsters, O. T. 1976, No. 75-636, pp. 24-25. However, National Motor Freight Agreements are of 3-year duration, and the 1970 Agreement was in effect when the complaint was filed. If a seniority system ceases to exist when the collective-bargaining agreement which creates it lapses, then the seniority system in Teamsters was adopted post-Title VII. On the other hand, if in practice the seniority system was continuously in effect from 1964, it can be argued that its adoption predates Title VII. However, Teamsters places no importance on the date the seniority system was adopted, and we follow Teamsters by refusing to distinguish among seniority systems based on date of adoption. Given the difficulty of determining when one seniority system ends and another begins and the lack of legislative guidance, we think it highly unlikely Congress intended for courts to distinguish between pre-Act and post-Act seniority systems.
  Justice Brennan’s dissent makes no mention of the importance which Congress and this Court have accorded to seniority systems and collective bargaining. It reads the legislative history as showing that Congress’ basic purpose in enacting § 703(h) was to protect employee expectations. Post, at 81-84. In doing so, it ignores the policy favoring minimal governmental intervention in collective bargaining.
  All parties agree that on remand the court should decide whether the lines of progression are part of a seniority system, and if so, whether they are bona fide within the meaning of § 703(h). We decline to reach those issues because, as the court below noted, their resolution requires additional factual development. See 634 F. 2d, at 749, n. 3.