Speaking of fighting the power, any attempt to stop Wal-Mart may seem downright futile. But if there’s cause for hope, it’s this case, which could turn into the largest class-action lawsuit in US history. It started back in June 2001 when a handful of East Bay women sued the box-store behemoth for on-the-job sex discrimination. They claimed that they’d been stuck in dead-end jobs while less-qualified men sailed into management positions. The lead plaintiff was Betty Dukes, a cashier from Pittsburg, who kept on working at Wal-Mart even as she took the company to court. One of her lawyers, Brad Seligman of the Berkeley-based Impact Fund, described her as “Wal-Mart’s worst nightmare.” Now the company’s worst nightmare is the prospect of half a million Betty Dukes. That’s how many women could end up suing it if a federal judge in San Francisco agrees to expand the suit into a nationwide class action. If he gives the go-ahead, every gal who has worked for Wal-Mart since 1998 could pile on, demanding billions in potential damages. (Women make up the bulk of Wal-Mart’s 1.1 million employees.) It’s still unlikely to slow Sam Walton’s relentless colonization of America, but it sure would be satisfying to watch the company get its Kathy Lee Collection slacks all in a twist.