Board of Governors of the Federal Reserve System: Is it legal for a business in the United States to refuse cash as a form of payment? [Useful information – I generally pay with cash and have increasingly encountered the response – we take credit/debit cards or you can use an app]
“Section 31 U.S.C. 5103, entitled “Legal tender,” states: “United States coins and currency [including Federal reserve notes and circulating notes of Federal reserve banks and national banks] are legal tender for all debts, public charges, taxes, and dues.” This statute means that all United States money as identified above is a valid and legal offer of payment for debts when tendered to a creditor. There is, however, no Federal statute mandating that a private business, a person, or an organization must accept currency or coins as payment for goods or services. Private businesses are free to develop their own policies on whether to accept cash unless there is a state law which says otherwise.”

See also The New York Times – Cash Might Be King, but They Don’t Care. [h/t Pete Weiss]