Me. Rev. Stat. Ann. tit. 9-A, §8-509
1. Surcharge prohibited. A seller in a sales transaction may not impose a surcharge on a cardholder who elects to use a credit card or debit card in lieu of payment by cash, check or similar means. For purposes of this section, "surcharge" means any means of increasing the regular price to a cardholder that is not imposed on a customer paying by cash, check or similar means. A discount or reduction from the regular price is not a surcharge.