Its NOT against the 'rules' for merchants to charge less for Cash versus Credit

I've seen people say more than once that its against the 'rules' for a business to charge more for use of a credit card versus cash. Around here its not uncommon to see gas stations charging one price for cash and then another price for credit. Charging less for cash transactions is perfectly OK under the rules of the credit cards.

From the Mastercard Rules for merchants page 5-9 states :
"A Merchant may provide a discount to its customers for cash payments."

From the VISA website:
"Can a merchant offer a discount for cash and check purchases? Yes."

Keep in mind these are only the policies of the credit card companies. So even if it was against the rules then the worst that could happen is the credit card companies would discipline the merchant in some way like dropping their account.