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What credit card information are offline US merchants allowed to collect for purposes other than the transaction? 
Zip code, as well as billing address, is used in conjunction with the Address Verification Service (AVS).  AVS is a web (or phone) service that actually verifies the address with the billing address on file with the issuing bank.  It does not use the credit card stripe.  You can see more information from various sources such as bank merchant help pages like Bank of America's. As far as what is stored on the stripe, it varies some by bank (as there are some "optional" areas).  The standards are discussed here. Fields include your account number, name, the expiration date, some card-specific stuff, and then the discretionary section.  I would not expect much in terms of address type information there. So - the answer to your question is that they can't really take much more than your name and CC #, unless you give it to them.  If you give a false zip code, you may have your purchase rejected.  They certainly do keep track of the credit card number, and I would suppose that is the most valuable piece to them; they can see you make purchases across time and know for a fact that it's the same exact person (since it's the same card). Additionally, zip codes for AVS from pay-at-the-pump are supposedly not generally used for marketing (see this article for example).  That is probably not true at at-the-register (in-person) collections, most of those aren't for AVS anyway.  Even California permits the pay-at-the-pump zip verification as long as it's only used for that (same article).  I would assume any information given, though, is collected for marketing purposes.