In a case with implications for businesses facing class-action lawsuits, the U.S. Supreme Court has agreed to hear arguments about whether six women employed by Wal-Mart Stores Inc. can represent 1 million of its workers.

The justices today said they will review a federal appeals court decision that approved a single suit to cover the claims of women who worked at the retailer’s 4,400 Wal-Mart and Sam’s Club stores since 2001. The suit, which threatens Wal-Mart with billions of dollars in liability, would be the largest-ever U.S. employment class action, Bloomberg reported.

Nineteen companies, including Bank of America Corp. and Microsoft Corp., urged the justices to take up the Wal-Mart appeal. They said the lower-court opinion makes it too easy for workers challenging employment practices to secure class-action status and then extract large settlements.

The lower-court ruling “would dramatically broaden the circumstances where classes can be certified in all types of cases against all types of companies,” Wal-Mart’s lawyer, Theodore Boutrous, said in an interview with Bloomberg.

Wal-Mart, the world’s largest retailer and the largest U.S. private employer, is accused in the 9-year-old suit of paying women less than men for the same jobs and giving female workers fewer promotions. Six women are seeking to serve as class representatives.