Imagine being hit with a discrimination case that involves millions of class members and potential damages in the billions of dollars. In the wake of a recent 9th Circuit decision upholding certification of the largest discrimination class action in history, Wal-Mart faces just that nightmare.

The case, originally filed in 2001 by six female Wal-Mart workers led by Betty Dukes, an employee at a Pittsburg, Calif., store, now includes all women who worked at any of the 3,400 U.S. Wal-Mart stores at any time since 1998. That’s potentially 2 million women, whom the suit alleges received lower pay and less opportunities than men.