“This was really a decision between helping out small business or helping out large banks,” said John Emling, a lobbyist for the Retail Industry Leaders Association. “No one wanted to pick between friends and they had friends on both sides, but because of the momentum, we just felt that if Durbin pushed folks to the vote we would win.”

The banking overhaul bill still needs to pass the Senate, and then it must be reconciled with a House bill that does not mention debit card “interchange” fees. Banking industry groups said that they had not given the issue enough attention in recent weeks, focusing instead on other controversial amendments. But they said they would now redouble efforts to convince legislators that the provision would hurt customers by undermining the debit card system.

“Retailers who benefit greatly from the system will pay almost nothing for the costs of maintaining and improving it,” said the American Bankers Association.

The Durbin amendment gives the Federal Reserve new authority to regulate and limit the fees that businesses pay to card companies. It specifically addresses payments processed through the Visa and MasterCard networks. American Express and Discover cards are not covered by the bill.

Last year businesses paid Visa and MasterCard $19.71 billion on debit card transactions, according to The Nilson Report, a trade magazine that is regarded as the best source of data on the industry. Visa and MasterCard in turn passed about 80 percent of the money, roughly $15.8 billion, to the banks that issued the cards.

The legislation directs the Fed to cap those fees at a level that is “reasonable and proportional” to the cost of processing transactions. The Nilson Report estimated that last year, fees averaged 1.63 percent of the transaction amount.

A second set of provisions applies to both credit and debit card transactions. Visa and MasterCard impose an all-or-nothing requirement on businesses, requiring them to accept cards even on small transactions, and prohibiting businesses from offering discounts based on the method of payment. The amendment strikes those rules.