NEW YORK ( TheStreet) -- A part of the financial-regulation bill, passed by the Senate yesterday, is a change in the interchange fee for debit cards. The change could benefit retailers but hurt banks and possibly harm consumers.Under the legislation, the interchange fee that retailers must pay issuers and banks for debit-card transactions would be decreased. Currently, that fee is about 2% of every transaction. According to a recent study by the Nilson Report, interchange fees paid by merchants for MasterCard ( MA) and Visa ( V) debit transactions totaled nearly $20 billion in 2009. The legislation would not affect the interchange fee levied on credit cards. How will interchange regulations affect consumers, retailers and banks? 1. Less convenient payments for small purchases. Credit cards make payments fast and easy, and we use them for the majority of our purchases regardless of the amount. Interchange regulations will allow retailers to set the minimum purchase price at $10 for credit card purchases. Shoppers must use cash for small purchases. While minimum payments may be inconvenient for consumers, permission to set minimum payments is good news for small retailers. Currently, retailers are required to accept cards for all purchases no matter how small the price. The minimum fees are so high that retailers often lose money on the small purchases with small profit margins. 2. Consumers may save money with cash discounts. Merchants will be able to offer discounts to people who pay with cash, checks or debit cards. However, the regulations do not require merchants to pass savings to consumers. 3. Lower prices could lead to lower debt. Interchange fees add approximately 2% to the price of goods. Ideally, merchants will lower prices if they don't have to pay the fee. But, again, retailers are not required to pass the savings on to consumers. 4. New or higher fees for bank accounts. Banks will lose billions of dollars from this change in interchange fees and they will look for new ways to replace that revenue. It is possible the decrease in interchange fee revenue could mean higher fee payments for consumers with bank accounts. Wells Fargo ended free checking account on July 1, and Bank of America ( BAC) is testing new fees to be added by the end of the year. Other banks may follow.