Wal-Mart Stores suffered a legal setback on Tuesday in its attempt to head off the biggest sexual discrimination case in United States history when an appeals court allowed the case to remain a class-action lawsuit.

The plaintiffs estimated they could win billions of dollars in lost pay and damages and that as many as two million women who have worked for Wal-Mart in its American stores since 1998 could join the suit.

But the court left open the option for Wal-Mart to file a new petition for a rehearing, and a Wal-Mart lawyer, Theodore Boutrous, said the retailer intended to do so.

The three-judge panel of 9th Circuit Court of Appeals said it would not reconsider its own decision affirming class certification to the case, but would allow both sides to appeal to the full court.

The revised ruling, which upholds a San Francisco federal judge's finding on class certification, allows the parties to file new petitions for rehearing.

Brad Seligman, a lawyer for Betty Dukes, the longtime Wal-Mart employee who brought the lawsuit in 2001, said in a statement that "the women at Wal-Mart are one step closer to their day in court."

Six other women have since joined the suit.

A three-judge panel ruled in a split decision in February that more than a million women could join a suit charging bias in pay and promotions.