Sen. Dick Durbin (D-Ill.) files an amicus brief with the Supreme Court, arguing for a lower Fed interchange cap.
Retail trade associations and two large retailers appeal to the Supreme Court to rule on the Federal Reserve's debit interchange rule.
National Retail Federation and other groups attacked the amount of debit card interchange allowed.
Retail trade associations and firms call the Fed's debit interchange rule an issue of staggering importance.
A Friday ruling allows retailers who opted out of last year's settlement to proceed with new suits. Card brands can also countersue retailers.
A new Aité Group report says cash is more expensive for retailers than cards. Retailer groups disagree.
E-commerce merchant Mitch Goldstone filed the interchange antitrust lawsuit back in 2005.
Credit cards still remain the most profitable loan product in the portfolio.
Plantiffs also say the sheer size of the debit card market make their case big enough for the nation's highest court.
Last year's lawsuit against the Federal Reserve could be heard by the Supreme Court.