Card network rules in the US prohibit merchants from adding a surcharge for payment with a debit card. Most merchants are either unaware, or prefer not to care. If you are using a debit card at a business that assesses a card surcharge, point out that your card is a debit card when paying and refuse to pay the surcharge. If that does not help, there are online forms available from both Mastercard and Visa where you can submit a merchant complaint.

The card processors policies are anti-competetive (albeit legal) abuses of their oligopoly. Reporting small vendors to them does not seem right to me.