In the latest skirmish in the 9-year legal battle over interchange fees, Wal-Mart, 7-Eleven and other retailers, joined by Senate Majority Whip Richard Durbin (D-Ill.), recently filed several briefs with the U.S. Supreme Court. The group seeks to change the Federal Reserve's cap on debit card interchange fees that took effect three years ago.

The retailers and the author of the Durbin Amendment, pictured at left, contend that the interchange fee cap was set higher than Congress intended when it passed the Dodd-Frank Consumer Protection and Wall Street Reform Act of 2010, according to court documents and sources involved in the case.

Wal-Mart and 7-Eleven, which opted out of the $7 million antitrust settlement with Visa and MasterCard, filed separate amicus briefs last week, arguing the Fed misinterpreted the legislation's intent and the fee cap should be lowered, said attorney Jeffrey Shinder, who represents 7-Eleven and a group of small ticket merchants involved in the litigation.