Credit unions have argued before U.S. District Judge Richard Leon in defense of the Federal Reserve's existing Durbin amendment regulation.

The arguments came in a friend of the court brief filed in a case that pits the group of retailers and retailer trade associations against the Federal Reserve. The group has filed suit against the Federal Reserve to force the regulator to cut the rate of debit card interchange more deeply than it did in the existing regulation.

Existing rules limit debit card interchange for all financial institutions, including credit unions, of over $10 billion in assets. The regulation also requires that debit card issuers, including credit unions of all asset sizes, carry two unrelated debit card networks to process their debit card transactions. This requirement was meant to prevent the processing networks tied to the two largest card brands, Visa and MasterCard, from dominating debit processing but CU critics have charged that the requirement effectively undermines a dual debit interchange structure the Durbin amendment meant to use to protect interchange for smaller asset CUs.