I'm a bit fuzzy on all the details as to time and place, but a few years ago mc/visa I believe tried to write into their merchant's agreements a provision requiring all transactions be done in local currency, as effective at that might be (after all their regulations require any valid card be honored). At least one of the payment processors sued that they couldn't do that and won the case. After that mc/visa hit on the idea because they make profits on foreign currency exchanges as does your bank, of converting their foreign currency fees to foreign transaction fees so it's now no skin off their rear ends whether one is dcc'd or not.