In the latest development of what has become a decade-long legal battle between merchants and credit card companies, several major retailers have rejected a $5.7 billion antitrust settlement. Now, a U.S. appeals court must decide whether to uphold its approval of the agreement between MasterCard and Visa and merchants despite the objections.

A lawyer for retailers including Target and Amazon urged the 2nd U.S. Circuit Court of Appeals in New York to reject the deal, saying it forces merchants to give up their rights to sue over various policies and practices.

"The defendants are trying to buy something that is not for sale," the lawyer, Thomas Goldstein, told Reuters.

On the other side, merchants who negotiated the deal believe it to be fair, providing more than just the $5.7 billion in damages, but reforms worth considerably more to merchants going forward.

This is not the first setback for the settlement, which addresses lawsuits going as far back as 2005 that accuse Visa and MasterCard of fixing interchange rates. At $5.7 billion, it is the largest ever in a U.S. antitrust class action. Originally, the settlement was for over $7 billion, but the amount was dropped after about 8,000 merchants, representing 25 percent of the transactional volume under scrutiny, opted out of the deal in 2012.

Dissenting retailers have maintained a worry that the agreement would do nothing to prevent credit card companies from raising interchange rates going forward (Although there are upper limits on merchant interchange fees for debit cards, no such caps exist for credit cards.). The agreement does allow retailers to pass the swipe fees on to customers, but merchants worry the extra charges would drive potential buyers away to rivals who would just pay the charges themselves.

The current appeal is still under consideration, with no timetable yet as to when a decision might be reached.