US retailers face a flood of sex discrimination cases if an appeal by Wal-Mart is dismissed by the courts.
Last week, a district attorney decided to give class action status to a suit brought by female workers over sex bias in pay and promotion.
Wal-Mart has appealed against the decision that opens the suit from a handful of women to an estimated 1.6 million workers past and present. It would make the class action the biggest in US history.
The case is expected to be a test for the retail sector, and other industries, in a country where female workers earn on average 77 per cent of the salary of male colleagues.
Wal-Mart payroll studies by the prosecution are reported to have revealed a 5 to 15 per cent gap in wages between women and men.
So far, no settlement figure has been suggested by lawyers.