SAN FRANCISCO (Bloomberg) — Wal-Mart Stores Inc. female workers suing the retailer for discrimination won a ruling that said more than 1 million women employees can collectively pursue claims seeking back pay in the biggest gender-bias case in US history.

A decision yesterday by a federal appeals court in San Francisco means women who have worked at Wal-Mart since 2001 can be part of a single class-action suit over discrimination claims, Brad Seligman, an attorney for the workers, said in a phone interview. Potential plaintiffs exceed one million, he said.

In a 6-5 ruling, the court sent claims for punitive damages and those of employees who had left Wal-Mart when the lawsuit was filed back to a judge in San Francisco for decisions about whether those allegations can be included in the group case.

"Wal-Mart tries to project an improved image as a good corporate citizen," said Seligman, a Berkeley, California, lawyer who is executive director of a non-profit law foundation focusing on civil rights and employement cases. "But no amount of PR is going to work until it addresses the claims of its female employees."

Greg Rossiter, a Wal-Mart spokesman, said the company would issue a statement on the ruling soon. Wal-Mart has 1.4 million US workers, according to company regulatory filings.

Wal-Mart, the largest private employer in the US, is accused of paying women less than men and giving them fewer promotions. The lawsuit was filed in 2001 by six women, including Betty Dukes, a Wal-Mart greeter in Pittsburg, California.

Wal-Mart, based in Bentonville, Arkansas, denied discriminating and said it should be allowed to fight the claims worker by worker.

Class status makes it easier for the group to finance the litigation than if the women proceeded individually. The women also have more leverage for a possible settlement.