The research, conducted among 21 retailers across the US, shows that 76% have not passed promised savings to consumers, despite already receiving $825 million in windfall profits in the first two months following the implementation of fthe Durbin amendment.

Congress justified the Durbin amendment, which established price controls on the cost retailers pay to accept debit cards, in part because of proclamations by retailers that consumers would benefit in the form of lower prices.

According to the EPC, 16 of 21 retailers visited across the country either raised prices or kept them the same before and after the October 1 implementation of the Durbin amendment, which slashed the price that retailers pay to accept debit cards in half.

Overall, customers paid on average 1.7% more after implementation, says Trish Wexler, spokeswoman for the Electronic Payments Coalition, singling out Wal-Mart and Walgreens as high profile transgressors.

"Merchants' empty promises to pass savings on debit card purchases are coming to light," she says. "More than two months after the Federal Reserve's rule implementation, customers are actually paying more for the same products - even though retailers are already taking home millions in additional profits."

These findings come just two weeks after the National Retail Federation, National Association of Convenience Stores, and other merchant organisations filed a lawsuit against the Federal Reserve, claiming that they should be paying even less in debit card interchange. The merchant groups are particular angered that the rule changes are hitting smaller stores, who have actually seen fees raised as card companies cut the discounted deals that were previously applied to small value transactions.