The U.S. Supreme Court heard arguments Tuesday on whether a massive class action lawsuit -- potentially the largest in U.S. history -- should be allowed to proceed that could see Wal-Mart pay hundreds of millions or more in damages to female employees.

Wal-Mart previously requested that the top court review the class certification of the long-running lawsuit, which began nearly 10 years ago when it was filed on behalf of employee Betty Dukes and five of her co-workers.

The U.S. Court of Appeals for the Ninth Circuit ruled in April 2010 that the class action, known as Wal-Mart Stores v. Dukes, No. 10-277, could proceed, though Wal-Mart's request has now brought the matter before the Supreme Court.

The lawsuit claims that men are favoured over women in pay and promotions at the 3,400 Wal-Mart and Sam's Club stores across the United States. It has been filed on behalf of at least 500,000 and possibly as many as 1.6 million female plaintiffs, which means that any payout -- or pre-emptive settlement -- would be enormous.

Dukes, a part-time cashier, said she has pursued the case "because I believe there was a pattern of discrimination, not just at my store, but across the country."

Wal-Mart denies that it discriminates against female employees and lawyer Theodore Boutrous Jr., told the court Tuesday that "there is absolutely no way there can be a fair process" when the company must defend its treatment of such a massive number of people working at thousands of different stores.

Gisel Ruiz said discrimination was not part of her experience as she rose up the ranks to become a vice president at the company.

"I've had a very positive experience at Wal-Mart, like thousands of other women," she said.

But Christine Kwapnoski, an assistant manager at a Sam's Club in Concord, Calif., said she was once told that raises only go to men with families to support.

"At that time I was a single mom with two children," she said. "I also had a family to support."

Several Supreme Court justices indicated that they are troubled by lower court decisions that allowed the case to proceed.

Joseph Sellers, a lawyer representing the women, said that lower courts were persuaded by evidence that has been compiled and put forth since the case was first filed in June 2001.

Sellers said the company has developed a corporate culture that stereotypes women as being less aggressive then their male peers, which has given way to the trend of discriminatory pay and promotion decisions at thousands of Wal-Mart stores.

"These decisions are informed by the values the company provides," Sellers said.

But Justice Anthony Kennedy said he is unsure "what the unlawful policy is" that Wal-Mart allegedly engaged in to discriminate against women.

"You said this is a culture where Arkansas knows, the headquarters knows, everything that's going on," Kennedy said to Sellers. "Then in the next breath, you say, well, now these supervisors have too much discretion."

Justice Antonin Scalia said that the company cannot be at fault in both ways.

Either individual managers are on their own, "or else a strong corporate culture tells them what to do," said Scalia.

Justice Ruth Bader Ginsburg said the issue at the moment is whether the case has enough evidence to go forward and not if discrimination could be immediately proven.

"We're talking about getting a foot in the door," Ginsburg said.

While Ginsburg said that Wal-Mart could refute the claims against it at trial, several of her colleagues appeared to suggest that subjecting the company to a trial would be unfair.

Members of the business community that side with Wal-Mart in the case say that allowing the lawsuit to proceed would permit discrimination cases to be brought forward with scant evidence. But proponents say if the court sides with the company, it will be more difficult for women and minorities to protect their rights in the workplace.

The court is expected to deliver a decision on the case by summer.

With files from The Associated Press