The Durbin amendment, implemented by Regulation II, is a provision of United States federal law, 15 U.S.C. § 1693o-2, that requires the Federal Reserve to limit fees charged to retailers for debit card processing. It was passed as part of the Dodd–Frank financial reform legislation in 2010, as a last-minute addition by Dick Durbin, a senator from Illinois, after whom the amendment is named.

After the rule to limit fees, 12 C.F.R. §235, went into effect, a coalition of merchants sued the Federal Reserve. The rule was upheld when the Supreme Court denied petition for certiorari in 2014. ^{[citation needed]}

Interchange fees or "debit card swipe fees" are paid to banks by acquirers for the privilege of accepting payment cards. Merchants and card-issuing banks have long fought over these fees. Prior to the Durbin amendment, card swipe fees were unregulated and averaged about 44 cents per transaction.

Merchants lobbied heavily for a rule to limit debit card swipe fees. They accomplished this when the Durbin amendment passed with the Dodd-Frank financial reform legislation on July 21, 2010. This was considered a major loss for banks, who receive billions of dollars a year in income from swipe fees.

The law applies to banks with over $10 billion in assets, and these banks would have to charge debit card interchange fees that are "reasonable and proportional to the actual cost" of processing the transaction. The bill aimed to restrict anti-competitive practices and encourage competition, and included provisions which allow retailers to refuse to use credit cards for small purchases and offer incentives for using cash or another type of card.

The Durbin amendment also gave the Federal Reserve the power to regulate debit card interchange fees, and on December 16, 2010, the Fed proposed a maximum interchange fee of 12 cents per debit card transaction, which CardHub.com estimated would cost large banks $14 billion annually. On June 29, 2011, the Fed issued its final rule, which holds that the maximum interchange fee an issuer can receive from a single debit card transaction is 21 cents plus 5 basis points multiplied by the amount of the transaction. This rule also allows issuers to raise their interchange fees by as much as one cent if they implement certain fraud-prevention measures. An issuer eligible for this adjustment, could therefore receive an interchange fee of as much as 24 cents for the average debit card transaction (valued at $38), according to the Federal Reserve. This cap—which took effect on October 1, 2011, rather than July 21, 2011, as was previously announced—reduces fees by roughly $9.4 billion annually. As a result, banks made plans to raise account maintenance fees to compensate.

The rule that the Federal Reserve issued went into effect on October 1, 2011 and capped the interchange rate paid to non-exempt card issuers at 0.05 percent plus twenty-one cents. The rule also allowed these non-exempt card issuers to earn an additional one-cent fraud prevention adjustment for implementation of fraud prevention policies.

Merchants and card-issuing banks opposed the Federal Reserve rule.