The retail group, which had not been part of the original litigation, had been criticizing the settlement for months.
Eleven states now ban retailer surcharges on credit card transactions.
Twenty-eight states either have bans or are considering them in wake of proposed antitrust settlement.
National Grocers Association was one of original litigants in the anti-trust case and now rejects the preliminary settlement.
U.S. Public Interest Research Group director downplays potential consumer impact; sides with merchants in surcharge snit.
Federal appeals court again rebuffs efforts to oppose interchange settlement until settlement is finalized.
Under interchange settlement, merchants can no charge for surcharges, but doubts remain if that will happen.
A CUNA survey of some of its member credit unions suggests credit unions with less than $10 billion in assets have begun to take a hit to their debit card interchange even though they were not supposed to feel the impact of a debit interchange cap.
Merchant Payments Coalition cites CUNA survey, says smaller-asset institutions shielded from interchange cap.
Card fight promises to go another round.