US Code
Part D— Credit Billing
§ 1666f. Inducements to cardholders by sellers of cash discounts for payments by cash, check or similar means; finance charge for sales transactions involving cash discounts

(a) Cash discountsWith respect to credit 11 So in original. Probably should be preceded by “a”. card which may be used for extensions of credit in sales transactions in which the seller is a person other than the card issuer, the card issuer may not, by contract or otherwise, prohibit any such seller from offering a discount to a cardholder to induce the cardholder to pay by cash, check, or similar means rather than use a credit card.
(b) Finance chargeWith respect to any sales transaction, any discount from the regular price offered by the seller for the purpose of inducing payment by cash, checks, or other means not involving the use of an open-end credit plan or a credit card shall not constitute a finance charge as determined under section 1605 of this title if such discount is offered to all prospective buyers and its availability is disclosed clearly and conspicuously.

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