Mr. Justice Black
delivered the opinion of the Court.
At issue in this case is the question whether elementary requirements of impartiality taken for granted in every judicial proceeding are suspended when the parties agree to resolve a dispute through arbitration.
The petitioner, Commonwealth Coatings Corporation, a subcontractor, sued the sureties on the prime contractor's bond to recover money alleged to be due for a painting job. The contract for painting contained an agreement to arbitrate such controversies. Pursuant to this agreement petitioner appointed one arbitrator, the prime contractor appointed a second, and these two together selected the third arbitrator. This third arbitrator, the supposedly neutral member of the panel, conducted a large business in Puerto Rico, in which he served as an engineering consultant for various people in connection with building construction projects. One of his regular customers in this business was the prime contractor that petitioner sued in this case. This relationship with the prime contractor was in a sense sporadic in that the arbitrator’s services were used only from time to time at irregular intervals, and there had been no dealings between them for about a year immediately preceding the arbitration. Nevertheless, the prime contractor’s patronage was repeated and significant, involving fees of about $12,000 over a period of four or five years, and the relationship even went so far as to include the rendering of services on the very projects involved in this lawsuit. An arbitration was held, but the facts concerning the close business connections between the third arbitrator and the prime contractor were unknown to petitioner and were never revealed to it by this arbitrator, by the prime contractor, or by anyone else until after an award had been made. Petitioner challenged the award on this ground, among others, but the District Court refused to set aside the award. The Court of Appeals affirmed, 382 F. 2d 1010 (C. A. 1st Cir. 1967), and we granted certiorari, 390 U. S. 979 (1968).
In 1925 Congress enacted the United States Arbitration Act, 9 U. S. C. §§ 1-14, which sets out a comprehensive plan for arbitration of controversies coining under its terms, and both sides here assume that this Federal Act governs this case. Section 10, quoted below, sets out the conditions upon which awards can be vacated. The two courts below held, however, that § 10 could not be construed in such a way as to justify vacating the award in this case. We disagree and reverse. Section 10 does authorize vacation of an award where it was “procured by corruption, fraud, or undue means” or “[w]here there was evident partiality .... in the arbitrators.” These provisions show a desire of Congress to provide not merely for any arbitration but for an impartial one. It is true that petitioner does not charge before us that the third arbitrator was actually guilty of fraud or bias in deciding this case, and we have no reason, apart from the undisclosed business relationship, to suspect him of any improper motives. But neither this arbitrator nor the prime contractor gave to petitioner even an intimation of the close financial relations that had existed between them for a period of years. We have no doubt that if a litigant could show that a foreman of a jury or a judge in a court of justice had, unknown to the litigant, any such relationship, the judgment would be subject to challenge. This is shown beyond doubt by Tumey v. Ohio, 273 U. S. 510 (1927), where this Court held that a conviction could not stand because a small part of the judge’s income consisted of court fees collected from convicted defendants. Although in Tumey it appeared the amount of the judge’s compensation actually depended on whether he decided for one side or the other, that is too small a distinction to allow this manifest violation of the strict morality and fairness Congress would have expected on the part of the arbitrator and the other party in this case. Nor should it be at all relevant, as the Court of Appeals apparently thought it was here, that “[t]he payments received were a very small part of [the arbitrator’s] income . ...” For in Tumey the Court held that a decision should be set aside where there is “the slightest pecuniary interest” on the part of the judge, and specifically rejected the State’s contention that the compensation involved there was “so small that it is not to be regarded as likely to influence improperly a judicial officer in the discharge of his duty . ...” Since in the case of courts this is a constitutional principle, we can see no basis for refusing to find the same concept in the broad statutory language that governs arbitration proceedings and provides that an award can be set aside on the basis of “evident partiality” or the use of “undue means.” See also Rogers v. Schering Corp., 165 F. Supp. 295, 301 (D. C. N. J. 1958). It is true that arbitrators cannot sever all their ties with the business world, since they are not expected to get all their income from their work deciding cases, but we should, if anything, be even more scrupulous to safeguard the impartiality of arbitrators than judges, since the former have completely free rein to decide the law as well as the facts and are not subject to appellate review. We can perceive no way in which the effectiveness of the arbitration process will be hampered by the simple requirement that arbitrators disclose to the parties any dealings that might create an impression of possible bias.
While not controlling in this case, § 18 of the Rules of the American Arbitration Association, in effect at the time of this arbitration, is highly significant. It provided as follows:
“Section 18. Disclosure by Arbitrator of Disqualification — At the time of receiving his notice of appointment, the prospective Arbitrator is requested to disclose any circumstances likely to create a presumption of bias or which he believes might disqualify him as an impartial Arbitrator. Upon receipt of such information, the Tribunal Clerk shall immediately disclose it to the parties, who if willing to proceed under the circumstances disclosed, shall, in writing, so advise the Tribunal Clerk. If either party declines to waive the presumptive disqualification, the vacancy thus created shall be filled in accordance with the applicable provisions of this Rule.”
And based on the same principle as this Arbitration Association rule is that part of the 33d Canon of Judicial Ethics which provides:
“33. Social Relations.
“. . . [A judge] should, however, in pending or prospective litigation before him be particularly careful to avoid such action as may reasonably tend to awaken the suspicion that his social or business relations or friendships, constitute an element in influencing his judicial conduct.”
This rule of arbitration and this canon of judicial ethics rest on the premise that any tribunal permitted by law to try cases and controversies not only must be unbiased but also must avoid even the appearance of bias. We cannot believe that it was the purpose of Congress to authorize litigants to submit their cases and controversies to arbitration boards that might reasonably be thought biased against one litigant and favorable to another.
Reversed.
“In either of the following cases the United States court in and for the district wherein the award was made may make an order vacating the award upon the application of any party to the arbitration—
“ (a) Where the award was procured by corruption, fraud, or undue means.
“(b) Where there was evident partiality or corruption in the arbitrators, or either of them.
“(c) Where the arbitrators were guilty of misconduct in refusing to postpone the hearing, upon sufficient cause shown, or in refusing to hear evidence pertinent and material to the controversy; or of any other misbehavior by which the rights of any party have been prejudiced.
“(d) Where the arbitrators exceeded their powers, or so imperfectly executed them that a mutual, final, and definite award upon the subject matter submitted was not made.
“(e) Where an award is vacated and the time within which the agreement required the award to be made has not expired the court may, in its discretion, direct a rehearing by the arbitrators.”
382 F. 2d, at 1011.
273 U. S., at 524.