Wal-Mart Stores asked the Supreme Court on Wednesday to review the largest employment discrimination lawsuit in American history, involving more than a million women workers, current and former, at Wal-Mart and Sam’s Club stores. Nine years after the suit was filed, the central issue before the Supreme Court will not be whether any discrimination occurred, but whether more than a million people can even make this joint claim through a class-action lawsuit... In April, the United States Court of Appeals for the Ninth Circuit in San Francisco ruled 6-5 that the lawsuit could proceed as a jumbo class action — the fourth judicial decision upholding a class action. The stakes are huge. If the Supreme Court allows the suit to proceed as a class action, that could easily cost Wal-Mart $1 billion or more in damages, legal experts say. More significant, the court’s ruling could set guidelines for other types of class-action suits... David Tovar, a Wal-Mart spokesman, denied that there was any companywide discrimination, saying that conditions had steadily improved for women employees