In a closely watched case, a sharply divided federal appeals court on Monday ruled 6-5 that a sex discrimination lawsuit against Wal-Mart Stores Inc. can proceed as a class action for at least one million women. The lawsuit is the biggest employment discrimination case in the nation’s history.

Legal tangle: Customers at a Wal-Mart store in Sao Paulo, BrazilPaulo Fridman/Bloomberg

“Wal-Mart tries to project an improved image as a good corporate?citizen,"?said?Brad Seligman, a lawyer for the plaintiffs. “No amount of PR (public relations) is going to work until it addresses the claims of its female employees."

The lawsuit, brought in 2001, accuses the retailer of systematically paying women less than men, giving them smaller raises and offering women fewer opportunities for promotion. The plaintiffs stressed that while 65% of Wal-Mart’s hourly employees were women, only 33% of the company’s managers were.

Wal-Mart said it disagreed with the ruling and would appeal to the US Supreme Court. It argued that the case should not proceed as a class action on the ground that any claims of discrimination involved largely individualized determinations rather than a group.

“We do not believe the claims alleged by the six individuals who brought this suit are representative of the experiences of our female associates," said Jeff Gearhart, general counsel for Wal-Mart, the country’s largest private sector employer, with 1.4 million employees. “Wal-Mart is an excellent place for women to work and fosters female leadership among our associates and in the larger business world."

Legal experts said the ruling would strengthen the plaintiffs’ leverage in settlement negotiations.

In the majority opinion, judge Michael Daly Hawkins wrote: “Although the size of this class action is large, mere size does not render a case unmanageable."

But the dissenting judges agreed with Wal-Mart and said that the case was too unwieldy for a class action.

“Never before has such a low bar been set for certifying such a gargantuan class," judge Sandra S. Ikuta wrote. Such a suit would leave large companies vulnerable “based on nothing more than general and conclusory allegations, a handful of anecdotes and statistical disparities that bear little relation to the alleged discriminatory decisions."

Wal-Mart said that Monday’s ruling could reduce the size of the certified class by as much as two-thirds, but Seligman said it would mean at most a one-fifth cut.

The ruling asks the district court to determine whether women who worked at Wal-Mart from 1998 to 2001, but no longer work there should be included in the class, which by some estimates can total at least two million women.

The lead plaintiff, Betty Dukes, applauded the ruling.

“It has taken a very long time, and a tremendous amount of work, but it looks like we’re finally going to get our day in court. That’s all we’ve ever asked for," she said in a statement.