Wal-Mart has petitioned the US supreme Court to intervene in a sex-discrimination case brought by its female workers.

The world's largest retailer is appealing an April ruling that authorised the class action, which could include more than 1 million women. According to the claims, Wal-Mart practiced broad discrimination in its pay and promotional decisions.

The Ninth Circuit Court of Appeals ruled in April that Wal-Mart should face charges in court that it pays women less than men for the same jobs. The lawsuit, which covers all female workers at the retailer since 1998 could cost the company billions if it loses.

Wal-Mart said that the "case involves important issues about class action procedure and Title VII and that the Ninth Circuit's opinion contradicts numerous decisions of other appellate courts and even the supreme court itself".

Despite the claims, Wal-Mart insisted that it is a good place for women to work. "Walmart is an excellent place for women to work and has been recognised as a leader in fostering the advancement and success of women in the workplace," it said in a statement.