Museum of Fine Arts doesn't actually want people using their discounted admissions for EBT card holders

I previously wrote about how cool the MFA's discount program is. Last week I was told that they don't accept debit/credit payment for the reduced admission. Their website doesn't say anything about this, but the person at the counter and the manager were both adamant about this, stating "we aren't set up to process transactions at that price point." This seems to violate the Dodd-Frank act, since businesses can require a minimum purchase of up to $10 for credit cards, but cannot do so for debit cards (four $3 EBT admissions to the MFA is $12). They do have an ATM in the building, but seemed unsympathetic to the fact that this would result in the ATM and my bank charging me fees that are as much as the ticket.

Here are the links for reporting them to MasterCard and to Visa for violation of merchant policies.