A $5.7 billion settlement by Visa and MasterCard was rejected by an appeals court in New York, potentially renewing years of litigation with U.S. merchants over allegations that credit-card swipe fees were improperly fixed.

The court said in its ruling that some retailers weren't adequately represented in the case.

"We are disappointed by today's ruling," Seth Eisen, a spokesman for MasterCard, said in an e-mailed statement. "We believe we presented a clear case to the court that the settlement was fair and appropriate based on more than four years of negotiation and the close involvement of the district court. We are reviewing the decision to determine our next steps."

Connie Kim, a spokeswoman for Visa, declined to comment.

Dozens of large retailers, including Wal-Mart Stores, Amazon.com and Target, as well as major airlines, health insurers and other consumer businesses criticized the deal. Some said the amount should have been higher and that a legal release preventing future lawsuits was written too broadly.

Visa declined 1.8 percent to $75.37 at 11 a.m. in New York, while MasterCard slipped 1.5 percent to $90.77. Visa and MasterCard were the first- and third-worst performers in the 68-company S&P 500 Information Technology Index.

U.S. District Judge John Gleeson approved the accord on Dec. 13, 2013, saying he was satisfied with the settlement, which was estimated to be the largest-ever U.S. antitrust deal.

Once owned by groups of major banks, Foster City, California-based Visa and Purchase, New York-based MasterCard have defended themselves for decades against legal claims that they operated price-fixing schemes. Swipe, or interchange, fees are set by Visa and MasterCard and paid by merchants when consumers use credit or debit cards.

Lawyers representing merchants nationwide announced the settlement in July 2012. Once worth as much as $7.25 billion, the settlement was valued at about $5.7 billion as of August 2013 as a result of reductions for about 8,000 merchants that dropped out of the damages portion of the lawsuit.

The case is In re Payment Card Interchange Fee and Merchant Discount Antitrust Litigation, 05-md-01720, U.S. District Court, Eastern District of New York (Brooklyn).

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