NEW YORK (CNN/Money) - Wal-Mart is expected Monday to ask a federal appellate panel to overturn a judge's order last year that allowed a sex-discrimination lawsuit against the company to proceed as a class-action suit, according to a published report Monday.

The Wall Street Journal reported that Wal-Mart (Research), the world's largest retailer, contends the case is too big for it to fairly defend.

The report said that if the order is upheld, Wal-Mart could face a lengthy court battle or, more likely, would pursue a settlement that by some estimates could cost the retailer billions of dollars.

On the other hand, the Journal cited legal experts who said if class-action certification is overturned, it would likely become too costly and cumbersome for the plaintiffs to pursue their cases individually.

The three-judge panel in the U.S. Ninth Circuit Court of Appeals in San Francisco could take months to issue a ruling, the paper said.

The sex-discrimination suit, filed in 2001 by six female workers, alleges that Wal-Mart systematically paid women less than men with similar qualifications, and frequently overlooked women for promotions, the report said.

A federal judge in San Francisco ruled last year that the lawsuit could apply to all women who have worked for Wal-Mart since December 1998, potentially affecting as many as 1.6 million current and former Wal-Mart employees.

The paper said Wal-Mart denied that it discriminates and maintains that any pay disparities were isolated.

In its appeal request, Wal-Mart argued that while the district court looked at companywide data, pay and promotion decisions are made by local managers on a store-by-store basis. The company said store-by-store statistics show that individual stores don't discriminate against women, the Journal said.

Wal-Mart lawyers are expected to argue that the complaints of six workers, supported by affidavits from an additional 100 current and former employees, aren't representative of the entire class of 1.6 million women, the report said.

The company said it should be able to defend itself on a case-by-case basis and that a class-action suit seeks payments for thousands of women who weren't victims of discrimination.

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