It's not "illegal". It's against their merchant agreement. No one is going to jail over it.

That said, the merchant agreement says you can't charge more for credit card users. But it doesn't say you can't give a discount for using cash. That's how my parents went around it.

It's illegal in this state just to charge more than, I think $1.50 or $2 or something, for that shit anyway. Would be funny if those stores really were some kind of illegal front and they get found out because of that law. Like Capone getting put away on tax evasion.