SAN FRANCISCO — A class action lawsuit charging Walmart with unequal pay for women who work at the discounter can go to trial, a federal appeals court has ruled.

A class action lawsuit charging Walmart with unequal pay for women who work at the discounter can go to trial, a federal appeals court has ruled.

In a 6-5 decision, the 9th U.S. Circuit Court of Appeals ruled that Walmart will have to face allegations that it pays women less than men for the same jobs and that women receive fewer promotions and have to wait longer for those promotions than men.

Walmart has contested the lawsuit — now the largest gender bias class action in U.S. history — since it was filed by six women in 2001 and says it will appeal the decision to the Supreme Court.

The ruling exposes every company in America to similar class actions, said Theodore Boutrous, the retailer’s lead lawyer in the case.

The appeals court upheld a lower court decision allowing the lawsuit to go forward as a class action, which lawyers for Walmart employees said comprises more than 1 million women. Walmart claims that fewer than 500,000 women can be included under the decision. Either way, the company could lose billions of dollars if it is found liable for back pay.

“The court significantly reduced the size of the originally certified class by as much as two-thirds,” Walmart executive vice president and general counsel Jeff Gearhart said in a statement. “Finding that the trial court ‘abused its discretion,’ the appeals court also set aside the ruling on punitive damages.”

Gearhart stressed that the court did not address the merits of the case, adding that the original plaintiffs’ claims were not representative of the experiences of the women who work at the discounter.

“We are proud of the strides we have made to advance and support our female associates, and have been recognized for our efforts to advance women through a number of awards and accolades,” he said, noting that in 2008 Walmart was named one of the “Top 40 Greatest Organizations for Women of Color to Work” by Women of Color magazine and one of the “Top 10 Best Companies for Women” by PINK magazine.