SAN FRANCISCO -- An assistant store manager at Costco Wholesale Corp. filed a federal civil rights lawsuit against the chain on Tuesday, alleging that she was passed over for a promotion because the company's policies discriminate against women in upper management.

The suit, which seeks class-action status to represent what plaintiffs lawyers say could be 650 women, claims that females rarely get high-level management jobs.

The lead attorney in the case, Brad Seligman, executive director of the nonprofit Impact Fund, is also suing Wal-Mart Stores Inc., alleging that the Arkansas-based retailer pays women lower wages and promotes them less than their male counterparts.

That case, which was granted class-action status, represents as many as 1.6 million current and former female Wal-Mart employees. But it is stalled in an appeals court and the merits have not been litigated.

The Costco case concerns Shirley "Rae" Ellis of Aurora, Colo., who was hired six years ago amid what she says were promises of a promotion within a year from her assistant manager post to an in-store manager at one of the chain's 320 U.S.-based outlets.

She said the bulks-good provider does not post job offerings for its managerial posts. "I would put my management ability against any manager," she said.

Issaquah, Wash.-based Costco, which employs about 103,000 people worldwide, released a statement that said: "We strongly disagree with any claim that Costco has discriminated against any individual or group of employees, and we will respond to this particular claim in the proper forum."

The suit, which focuses on in-store assistant manager and manager positions, claims that 50 percent of the chain's employees are female but the management "is virtually all male." The suit says only 12 percent of Costco's store managers and two of 30 upper-level executives are women.

Ellis is seeking unspecified damages, including lost wages, and wants the company to post its managerial positions to its employees.

No hearing has been set for a judge to determine whether the lawsuit will represent all current and former female employees who might have been wrongly passed over for a promotion to assistant manager or manager.

Assistant managers receive about $65,000 or more, and managers get more than $100,000 plus bonuses, according to Seligman. He said the suit was about "changing the way Costco does business."

Costco shares rose 49 cents to close at $41.31 Tuesday on the Nasdaq Stock Market.