March 28, 2011 -- When Christine Kwapnoski of Concord, Calif., told her boss at a division of Walmart that she wanted a job promotion, she said, he told her to "blow the cobwebs off your make up" and to "doll up" in order to advance.
Instead, she joined five other female employees and filed a sexual discrimination suit against the company 10 years ago alleging that women had been paid less than men in comparable positions in violation of Title VII, the federal law that prohibits sex discrimination.
As word of the suit spread, dozens and dozens of women joined in and a lower court ruled that the case could go forward on behalf of all current and former female employees since 1998.
Kwapnoski will be at the Supreme Court Tuesday when the justices hear arguments on whether the lower court was correct in allowing the women to band together to file their lawsuit, or whether they must file as individuals.
If the court rules in favor of the women and grants them "class certification," it will most likely become the largest employment class-action suit in history, involving potentially millions of women and billions of dollars.
A decision is likely to come in early summer.
Kwapnoski said she would never have been able to file the suit alone against the world's largest corporation. "My voice against Walmart?" Kwapnoski asked. "Are you kidding me. They would sweep me under the carpet real fast. When we band together, then Walmart has to listen to us."
Walmart has dismissed the claims of sex discrimination. Gisel Ruiz, the executive vice president of human resources at the Bentonville, Ark.-based company, said the company has a long history of providing advancement opportunities for women.
"Thousands of women began their careers at Walmart," Ruiz said," and have risen to leadership roles."
Walmart has also argued that the lower court was wrong to allow the women to join together in their lawsuit because they don't satisfy the "commonality requirement" that is required to prove that the women have enough in common to proceed as a class.
Walmart has 3,400 U.S. stores and 170 different job classifications.
The plaintiffs cannot fairly represent "over 1.5 million other women who worked for thousands of different stores with thousands of different managers in multiple states throughout the country," Ruiz said.
Businesses Worry About Potential Fallout
The case is being carefully watched by the business community, which fears that it could lead to an increase of similar suits and force big business into premature settlements out of fear of exposure to gigantic monetary awards in the billions of dollars.
The Chamber of Commerce has issued a brief on the side of Walmart, arguing that the lower court ruling that allowed the case to go forward as a class action "will likely encourage an avalanche of new class-action litigation on a broad array of subject matters, beyond employment issues."
But lawyers for the women say such fears of an avalanche are absurd. "The reality is that we haven't even had a few snowflakes" said Joseph Sellers, who will argue on behalf of the women.
The district court heard months of evidence in the case and properly found that the women had met the standards of class certification, he said.
"The Supreme Court and the lower courts have set very demanding standards for class certification," he said.
Sellers and civil rights groups supporting the women have said that class-action certification is essential to giving anti-discrimination laws the force and intent they were meant to have. They argue that the women, forced to file individually, would have neither the means nor the incentive to bring their cases against such a large company.
Although the justices won't wade into the merits of the case regarding gender discrimination, Sellers said, the question of whether the women can proceed as a class action is of equal importance.
"Technically, this case is not a ruling on the merits, but the ability to pursue claims like this is vital to the private enforcement of civil rights laws," Sellers said.
Lawyers for the women say that besides the anecdotal evidence, statistical analysis demonstrated that hourly and salaried retail female employees received lower pay and less advancement opportunities than their male counterparts.
Plaintiffs Stand by Their Statistics
"The patterns are inescapable," Sellers said. "This is not simply a case where you group together a bunch of independent decision makers. It shows a pattern that is stunning in its consistency showing that women were uniformly disadvantaged."
He said Walmart managed its operations and employment practices in a centralized manner, despite doing business in stores across the country. But company lawyers say the statistical analysis provided by the plaintiff's experts is wrong.
"In Walmart's retail stores, women made up two-thirds of all employees and two-thirds of all managers," Theodore J. Boutrous Jr., who will argue the case for Walmart Tuesday, said. "The record actually shows that the number of women who were promoted at Walmart was equal to or greater than the number who applied for the jobs.
"Plaintiffs' data is deeply flawed and highly misleading. Where the data runs counter to their theory, they simply disregard it or relabel it to obscure the major gaps in their case."
Timothy Sandefur of the Pacific Legal Foundation, who submitted a brief in support of Walmart, disagrees with the lower court's reliance on statistical analysis provided by the plaintiffs to document what they say is widespread discrimination at the company.
"There's all sorts of reasons why people might choose to work in other jobs, or choose to not work as managers or stay out of the work place for a long time that are not proof of discrimination," he said.
But Sandefur's argument enrages some of the women's rights group supporting the Walmart plaintiffs.
"Statistical evidence demonstrates that even if you control for job performance and seniority, pay discrepancies existed at all the major job groups within Walmart," Sarah Crawford of the National Partnership for Women and Families said.
"These women are seeking to vindicate their civil rights, their rights to fair pay and promotions at Walmart in the face of a great deal of evidence that systemic discrimination was standing in their way. We are still trying to get our day in court."
ABC News' Susanna Kim contributed to this report.