1. All merchants who want to do this have to post a clearly written notice on their front doors (or at the register) stating the %amount of the fee. Or at the time of the transaction the fee has to be clearly stated as a Processing Fee - it cannot be hidden as something else. Web sites have to clearly state the fee either on their home page or on the checkout page when you start to enter card information.
2. As stated 10 states cannot charge the fees due to state laws. If you are at a retailer that does business in those 10 states then they cannot charge a fee in your state as the rules state that if they charge fees in one state, they have to charge them in ALL states.
3. Law says you if you charge a fee for one credit card (say a visa) you have to charge the same for all credit cards (MasterCard, Amex, Discover, etc). Amex rules state that charging a fee is against their rules, so if they take Amex, they cannot charge a fee.
4. All major retailers, etc. stated that they had no plans to start charging a fee.
5. Fee has to be clearly listed as a Processing Fee and cannot be hidden as to what it is. In fact Visa/MasterCard rules have always prohibited adding any fees to your charges to cover the card/bank fees. You were only allowed to add fees required by law (such as environ fee for tires, batteries, etc.).
6. The fee can only be for the actual amount the merchant pays as a processing fee. If they are charged 1.5% then they can only charge the customer 1.5% - they cannot just charge a blanket 4%.
7. These rules haven't even been approved by the courts - the case and even deal are taking so long, that the initial time to allow this fee came around and the deal hasn't been approved. If the judge says NO, then it could all go away again.
8. Most people have never read the rules that Visa, MasterCard, and Amex have over the retailers that take them. You really should because you have a lot of coverage and the card companies will investigate any violations reported to them. And I highly suggest that if you see a merchant violating the card rules, you report them.