A federal appeals court ruled Tuesday that Wal-Mart Stores Inc., the world’s largest private employer, must face a class-action lawsuit alleging female employees were discriminated against in pay and promotions.

The ruling by the 9th U.S. Circuit Court of Appeals upholds a 2004 federal judge’s decision to let the nation’s largest class-action employment discrimination lawsuit go to trial. The suit claims that as many as 1.5 million current and former female employees earned less than men and were bypassed for promotions.