A federal judge in the United States this week Tuesday ruled that a sex discrimination case against Wal-Mart, the world's biggest retailer, can be pursued as a class action lawsuit. The suit could involve 1.6 million American women.

It would be the largest sex-bias lawsuit in history and the largest class action suit brought against a private U.S. employer. The case was brought three years ago by six Wal-Mart female employees who claim they were denied pay and advancement routinely offered to their male counterparts. Susan Medolo is one of the plaintiffs. She tells the NBC Today program that discrimination still continues at Wal-Mart.

"Definitely. I have a girl friend who has worked at the company over 15 years. And I won't give the exact number of years because they might find out who she is. And she is a cashier and she has been discriminated against," she said. "She is making less than $11 an hour."

Stephanie Odle, another plaintiff, was a manager at Wal-Mart in the 1990s. She says a male counterpart was being paid much more than she was being paid, on the grounds that he had a family to support. When she complained she got a raise. She was grateful, she says, until she thought more about it.

"And then it took me a little while to realize, hello?, he was making $20,000 more a year than you and you just got a $2,000 raise," she said.

Wal-Mart denies the charges and will appeal the federal court ruling. It points to its hundreds of female managers. Wal-Mart's share price on the New York Stock Exchange has fallen for six consecutive days, in part because of concerns about the potential cost of the lawsuit. But consumer brand analyst Robert Passikoff in New York says the case is unlikely to have much impact on Wal-Mart customers.

"The degree to which the corporation meets its legal obligations in terms of employment really only accounts for about three percent of overall customer loyalty in driving profitability for the brand [Wal-Mart]," he said.

This legal action against Wal-Mart is likely to take several years to resolve. The largest sex-discrimination case in the United States involved the U.S. government branch that oversaw the Voice of America, which four years ago was found guilty of gender bias and had to pay 1,100 women $460,000 each. The case cost the U.S. government $500 million.