WASHINGTON (AP) — The Supreme Court said Monday it will consider whether to keep alive the largest employment discrimination lawsuit in U.S. history, a case that claims Wal-Mart pays women less than men and promotes women less frequently.

The justices stepped into a dispute that could involve billions of dollars in back pay for 500,000 to 1.5 million women who work or once worked at Wal-Mart Stores Inc., the world’s largest private employer. But the case also could affect other class-action lawsuits, in which people with similar interests increase their leverage by joining together in a single claim.

Wal-Mart, backed by many business interests, praised the court’s intervention.

“The current confusion in class action law is harmful for everyone — employers, employees, businesses of all types and sizes, and the civil justice system,” the company said in a statement. “These are exceedingly important issues that reach far beyond this particular case.”

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Wal-Mart is appealing a ruling by the 9th U.S. Circuit Court of Appeals in San Francisco that the class-action lawsuit could go to trial.

The company says that allowing the large number of claims to go forward would set off an avalanche of similar class-action lawsuits in California and the other Western states overseen by the 9th Circuit.

But the lawyers representing the women who are suing Wal-Mart say there have been only eight such suits nationwide — and none within the 9th Circuit — since the first appeals court ruling in favor of the women nearly four years ago. “This threatened landslide of class-action litigation has not materialized,” the lawyers said in legal papers filed with the Supreme Court.

Wal-Mart employs 1.4 million people in the United States and 2.1 million workers in 8,000 stores worldwide. The company said the women should not be allowed to join together in the lawsuit because each outlet operates as an independent business. Since it doesn’t have a companywide policy of discrimination, Wal-Mart argued that women alleging gender bias should file individual lawsuits against individual stores.

The plaintiffs contend that the company was aware that it lagged behind other employers in terms of opportunities for women and that Wal-Mart imposes uniform rules and tight controls over its stores.

The lawsuit was first filed by six women in federal court in 2001. The 9th Circuit has three times ruled that the case could proceed as a class action.

The case will be argued in early 2011.

Copyright 2010 The Associated Press.