|As of Sunday, merchants can begin charging you the consumer the fee they are charged by the processing companies. Maximum is 4%, but that can be a lot. Forewarned is forearmed, so pay attention when you go in a store.|
And they can add the charge later, after you have left their store.
There are some states where this will not be happening.
States that WILL NOT charge the “checkout fee” due to state law:
Connecticut New York