In the US, there was never such a law. It was a term of credit cards' merchant agreement that merchants couldn't charge extra for credit card use.
However, the recent Dodd-Frank Act limits that - merchants can give a discount for using cash and allows them to set a minimum amount for credit cards up to $10.
However, the recent Dodd-Frank Act limits that - merchants can give a discount for using cash and allows them to set a minimum amount for credit cards up to $10.