Google says:

Starting in 2013, it became legal to charge customers extra for using a credit card. Retailers can also require a minimum purchase amount when you use credit cards. But merchants need to follow specific rules when adding credit card surcharges.

Eleven states—California, Colorado, Connecticut, Florida, Kansas, Maine, Massachusetts, New York, Oklahoma and Texas—and Puerto Rico have laws that prohibit merchants from charging consumers with surcharges on credit card transactions.