Filed at 11:09 a.m. ET

SAN FRANCISCO (AP) -- A federal judge on Tuesday approved class-action status for a sex-discrimination lawsuit against Wal-Mart Stores Inc. that has become the largest private civil rights case in U.S. history.

It could represent as many as 1.6 million current and former female employees of the retailing giant.

The suit alleges Wal-Mart set up a system that frequently pays its female workers less than their male counterparts for comparable jobs and bypasses women for key promotions.

Wal-Mart, the nation's largest private employer and the world's biggest retailer, sought to limit the scope of the lawsuit filed in San Francisco three years ago.

Wal-Mart spokeswoman Mona Williams told The Associated Press on Tuesday that the Bentonville, Ark.-based company will appeal the ruling and is confident it does not discriminate against women employees.

U.S. District Judge Martin Jenkins took nine months to decide whether to expand the lawsuit to include virtually all women who work or have worked at Wal-Mart's 3,500 stories nationwide since 1998. His ruling makes the lawsuit the nation's largest class action. A trial date has not been set.

``I think it's a terrific victory for the women who work at Wal-Mart who have labored for years under working conditions where they have been told repeatedly they have been unsuitable for management and not suitable to make as much as men,'' said Joseph Sellers, one of the attorneys representing the women.

But Wal-Mart's Williams said, ``Let's keep in mind that today's ruling has absolutely nothing to do with the merits of the case. Judge Jenkins is simply saying he thinks it meets the legal requirements necessary to move forward as a class action. We strongly disagree with his decision and will appeal.''

In a daylong hearing in September, company attorneys urged Jenkins to allow so-called mini-class action lawsuits targeting each outlet. Wal-Mart contends its stores, including Sam's Club warehouse outlets, operate with so much autonomy that they are like independent businesses with different management styles that affect the way women are paid and promoted.

Pursuing the allegations as a single class action ``is absolutely unmanageable on a nationwide basis,'' Wal-Mart lawyer Paul Grossman argued to Jenkins. ``It would require a mind-boggling number of individual determinations.''

But Jenkins ruled that a 1964 congressional act, passed during the civil rights movement, prohibits sex discrimination and that giant corporations are not immune.

In addition, the judge said the women put on enough anecdotal evidence to warrant a class-action trial.

Jenkins decided that the ``plaintiffs present largely uncontested descriptive statistics which show that women working at Wal-Mart stores are paid less than men in every region, that pay disparities exist in most job categories, that the salary gap widens over time, that women take longer to enter management positions, and that the higher one looks in the organization the lower the percentage of women.''

Jenkins found that the evidence so far ``raises an inference that Wal-Mart engages in discriminatory practices in compensation and promotion that affect all plaintiffs in a common manner.''

In morning trading on the New York Stock Exchange, Wal-Mart shares were down $1.02, or nearly 2 percent, at $53.91.