Me. Rev. Stat. tit. 10, § 1142

When a travel agent furnishes travel services to a consumer and the consumer uses a credit card to obtain credit in the transaction, the provider of travel services for which the travel agent is an agent may not as the result of the use of the credit card impose a surcharge on or reduce commissions paid to the travel agent. This prohibition does not apply if the provider of travel services is the issuer of the credit card used in the transaction.