Comment by mdaniel

It used to be a violation of their merchant agreement but it seems a 2013 court case made it that as long as it's disclosed in a certain way, it seems to be ok. About 4 states still outlaw it, based on some digging, but none of the card rules that I could dig up allowed applying that fee to debit cards containing the logo (e.g. https://www.mastercard.us/en-us/business/overview/support/me... )