However, federal law caps it at 4%, and major card networks restrict it to 3% to 4%, so the lower federal/network limits must be followed.

This is the kicker here since the MasterCard Network limits to the lower of the actual cost of fees to process the transaction or 4%.  I have had a few businesses in Minnesota charge 4.5-5% and I have pointed out they should switch to Square to which I get a response that Squares fees are too high.

Earlier this year I pointed out to business that their fees are too high and in violation of card processor agreements and they flat out told me they don't care because MN said up to 5% so that is what they do.  I finally reached a breaking point since they are charging more than they should both legally (over fedral limit) and civilly (over card processor limit) so I reached out to my cards customer service and they said I need to dispute the charge with reason as incorrect amount.  Since I know Square charges 2.6% + 15c (or less) and they claim they are too high it is safe to assume they pay less than 2.6% so I have begun disputing charges when the CC fee is above 2.6% when I point out to them they are violating the Mastecard terms and they tell me they don't care; some businesses state they did not know that and they will look into it and I often see them post lower CC surcharge in a few months.  It is one thing to be ignorant and another to blatantly disregard laws and agreements.

I am pretty certain the CC companies want the surcharges gone since it discourages use of their product and is why they have terms to limit the surcharges so customers will continue choosing card over cash/check/ACH.