It's not illegal, but it is against Visa and Mastercard's rules, to levy a fee or surcharge to use a credit card. What IS illegal is to prohibit merchants from offering a discount to induce customers to pay by cash or check, which is why merchants that do so don't end up having their Visa and Mastercard contracts cancelled.

>Which they don't and also it's illegal

source? because there are tons of gas stations that offer a "cash price" and a "debit/credit card" price.