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.
"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.