Two instead of four unaffiliated payment networks could be required as result of federal judge's ruling.
Trades also indicate possible appeal after federal court throws out Fed's 21-cent cap.
Federal judge throws out Durbin Amendment's 21-cent cap in emphatic ruling.
The question of whether or not the Federal Reserve went far enough or too far in capping debit card interchange in accord with the Durbin amendment went before a U.S. District Court Judge recently.
Retailers, issuers to face off again in court Tuesday over interchange rate.
Credit unions have argued before U.S. District Judge Richard Leon in defense of the Federal Reserve's existing Durbin amendment regulation.