Lawyers representing the plaintiffs recruited Ms. Odle after obtaining a data showing that just a third of Wal-Mart’s managers were women even though two-thirds of its employees were. The lawyers wanted to enlist a Wal-Mart employee whose complaints about pay and promotions would be a base from which to build a broader sex discrimination case.

Ms. Odle’s story, along with those of six other women, became the seed of the 2001 lawsuit that accused Wal-Mart of systematic discrimination against women in pay and promotions. No one expected it to become such a drawn-out battle.

In its appeal, Wal-Mart said the Ninth Circuit’s decision had contradicted earlier decisions of the Supreme Court and other appeals courts and had wrongly relieved the plaintiffs of the burden of proving individual injury.

“This conflict and confusion in class-action law is harmful for everyone  employers, employees, businesses of all types and sizes, and the civil justice system,” said Theodore Boutrous, a lawyer for Wal-Mart.

In its filing, Wal-Mart argued that while a class action might be appropriate for plaintiffs seeking changes to the retailer’s behavior, the status was improper for seeking monetary damages.

The company said the complaints of the seven women were not typical of the more than one million women who have worked at Wal-Mart in the last decade. In a statement Wednesday, Wal-Mart said that it “has been recognized as a leader in fostering the advancement and success of women in the workplace.”

Brad Seligman, a lawyer for the women, disputed Wal-Mart’s legal analysis. “The ruling upholding the class in this case is well within the mainstream that courts at all levels have recognized for decades,” he said in an e-mail Wednesday. “Only the size of the case is unusual, and that is a product of Wal-Mart’s size and the breadth of the discrimination we documented. There is no ‘too big to be liable’ exception in civil rights laws.”