For more than 25 years U.S. merchants were prohibited from setting a minimum credit or debit card purchase amount. Visa, MasterCard and Discover adopted rules to penalize merchants who typically set a $10 minimum for credit or debit card use. However, under the Dodd-Frank Wall Street Reform and Consumer Protection Act, it has changed somewhat. Merchants can now set up to a $10 minimum on a credit card purchase. However, merchants are still prohibited to set a minimum for a debit card. Best advice is to still carry a little mad cash or use your debit card for the small stuff.