A U.S. District Court judge gutted the Federal Reserve's debit card regulatory regime July 31, ruling the Fed rule disobeyed the law and ordering the regulator to rewrite it.

Judge Richard Leon's comprehensive and often sarcastic 58-page opinion overturned the Fed's 21-cent cap on debit card interchange for issuers of more than $10 billion in assets and scrapped the Fed's requirement that all debit card issuers participate in at least two unaffiliated payments networks.

Both the cap and the unaffiliated network regulations flowed from the Durbin amendment, a piece of legislation that credit unions strongly opposed which was attached at the last moment to the 2010 Dodd-Frank regulatory reform law.