Wal-Mart Stores Inc. and Starbucks Corp. are among 19 retailers opting out of a $7.25 billion antitrust settlement with Visa Inc. and MasterCard Inc. over fees charged to merchants to process credit-card transactions.

The proposed settlement would maintain and strengthen an anticompetitive system that allows Visa and MasterCard to fix so-called swipe fees for banks, the companies said Tuesday.

"It would allow credit card companies and big banks to perpetuate an unfair and broken system that costs all consumers," Mike Cook, senior vice president of finance for Wal-Mart, said in a statement.

The settlement, estimated to be the largest-ever U.S. antitrust accord, has drawn criticism from trade associations and retailers contending that it grants the card companies too much leeway to raise rates.

Visa and MasterCard agreed to settle the case to resolve the legal battle over interchange fees, which are charged to merchants when customers pay with credit cards.

The settlement received tentative approval from a federal judge in New York in November. A hearing on final approval is set for Sept. 12.

The Electronic Payments Coalition, which represents Visa, MasterCard and banks and credit unions that issue payment cards, said it is confident that the objection from the companies will have "no material impact" on final approval.

"These same tired arguments were already raised repeatedly over the course of the litigation," said a spokeswoman, Trish Wexler.

K. Craig Wildfang, an attorney for plaintiffs in the case, said the announcement by Wal-Mart and others wasn't surprising.

"These merchants have been publicly critical of the settlement, and we always thought that many of them were likely to opt out," said Wildfang, of Robins, Kaplan, Miller & Ciresi. "We remain confident that the vast majority of merchants in the class will not opt out."

Other companies joining Wal-Mart and Starbucks on Tuesday include Gap Inc., Lowe's Cos., Costco Wholesale Corp. and Nike Inc., according to the statement.