A top lawyer for the U.S. Federal Reserve said the regulator plans to appeal a ruling by a federal court judge in late July that overturned a cap on debit card swipe fees.

The debit card swipe fee rule was mandated by the 2010 Dodd-Frank Wall Street reform law. It calls for limiting the fees that banks charge merchants when customers use debit cards. A retailer trade group had challenged the Fed's rule, saying the cap was set higher than Congress had intended.

Scott Alvarez, the Fed's General Counsel, told a judge in court on Wednesday that the Fed will seek to keep the rule in place while it appeals the case.