"Two courts now have ruled that Wal-Mart is going to have to face a jury... We fully expect Wal-Mart to keep appealing but we're very confident now that two courts have upheld this [class] certification," he said.
Lead plaintiff Betty Dukes, 56, who works as a greeter at a Wal-Mart east of San Francisco, said she had let out a cheer while at work. "I am absolutely overjoyed," Dukes said.
The two-one ruling by the three-judge panel of the court of appeals took no position on Dukes's claims, stressing the decision only affirmed a lower court ruling to certify the case as a class action against the world's largest retailer.
Wal-Mart has been a lightning rod for controversy, accused of underpaying workers and undermining small business with its huge stores- charges it has denied, pointing to itself as a major source of jobs.
The company said it would appeal against the ruling.
"This was one step in what is going to be a long process, and we are still at a very early stage in this case," said Ted Boutrous, lead counsel for Wal-Mart's appeal.
"We are very optimistic about our chances for obtaining relief from this ruling as the case progresses."
In a class action, individuals bring a suit on behalf of a larger group that suffered similar harm. In the Wal-Mart case, six other women join Dukes as the plaintiffs.
Dukes, a Wal-Mart employee for nearly 13 years, said she sued the company because of neglect she and fellow female employees felt when openings for positions were advertised within her store.
After working as a cashier for three years, Dukes said she advanced to a customer service representative post, a promotion that some male employees obtained even before their probationary periods expired.
"I had seen males go into the position with less than 90 days experience," Dukes said.
Bentonville, Arkansas-based Wal-Mart had argued it did not discriminate and that class-action status should be dismissed because the company grants its 3,400 US stores a great deal of independence in their management.
Donald Gher, chief investment officer of Coldstream Capital Management, which owns Wal-Mart stock, said the decision was a setback for the retailer and would cheer the company's critics in the US labour movement.
"Clearly this is a big win for the tort lawyers and for the unions who are looking to cases like this to help bolster their ranks," he said.
Shares of Wal-Mart were little changed on the news, and closed six cents higher onTuesday at $48.58 on the New York stock exchange.