WASHINGTON (AP) -- The Supreme Court on Monday blocked a massive sex discrimination lawsuit against Wal-Mart on behalf of female employees in a decision that makes it harder to mount large-scale bias claims against the nation's biggest companies.

The justices all agreed that the lawsuit against Wal-Mart Stores Inc. could not proceed as a class action in its current form, reversing a decision by the 9th U.S. Circuit Court of Appeals in San Francisco. By a 5-4 vote along ideological lines, the court said there were too many women in too many jobs at Wal-Mart to wrap into one lawsuit.

The lawsuit could have involved up to 1.6 million women, with Wal-Mart facing potentially billions of dollars in damages.

Now, the handful of women who brought the case may pursue their claims on their own, with much less money at stake and less pressure on Wal-Mart to settle. Two of the named plaintiffs, Christine Kwapnoski and Betty Dukes, attended the argument. Kwapnoski is an assistant manager at a Sam's Club in Concord, Calif. Dukes is a greeter at the Walmart in Pittsburg, Calif.

In a statement, Wal-Mart said, "The court today unanimously rejected class certification and, as the majority made clear, the plaintiffs' claims were worlds away from showing a companywide discriminatory pay and promotion policy."

Dukes and Kwapnoski said they were disappointed in the ruling, but vowed to push ahead with their claims. Both women spoke on a conference call with reporters.

"We still are determined to go forward to present our case in court. We believe we will prevail there," Dukes said.