You don't, actually. It's illegal to charge an additional fee for using a card. It's legal to offer a discount for cash, however. Not only that but the fees charged per card are different depending on the card and the banking network it's processed through. The debate about coffee shops taking bitcoin is all about the access, as per usual. If Square ran on BTC your local coffee shop would run on BTC. The problem is that BTC is becoming cumbersome for anything but big transfers; it's starting to look more like a bad implementation of ACH and less like a peer-to-peer network (more Spotify, less Pirate Bay). If you're going to put up with something cumbersome, why not stick with the FDIC-insured, not-taxed-as-property alternative known as "money?"
Correct me if I'm wrong (Wintermute), but I'm assuming she/he meant that prices are raised proportionally for everybody by places that accept credit to make up for the fees they have to pay, so you're paying a shop's credit card fees whether you're paying by credit or not. I can't imagine that it's illegal in this situation, but I have no idea about the law you're referencing.
I'm aware that's what they meant. I was pointing out that it's a facile argument. On the one hand, you might as well assume the fees are "baked in" from the pastry delivery charges, or the extra time necessary to make a pour-over, or the electrical bill. There's certainly overhead associated with a credit card, but if you add it in in any way visible to the customer, Visa, Mastercard and Amex will all revoke your agreement. Also, any sorts of charges are flatly illegal in 10 states. On the other hand, cash discounts are entirely legal. So is that discount "baked in?" If the shop offers no cash discount (most commonly seen at gas stations), the answer is no. Even though it's perfectly legal. Even though credit card transaction fees are usually between 3% and 7%. So - variable overhead you are explicitly forbidden from outlining vs. fixed overhead you are explicitly permitted to outline. "baked in" is a dumb way to describe it.