WASHINGTON (AFP) - The US Supreme Court on Monday unanimously rejected a class action suit against retail giant Wal-Mart by 1.5 million female workers who claimed they had been systematically discriminated against on the basis of gender. The top US court ruled that Wal-Mart had no overarching employment policy so the women could not all have suffered discrimination for the same reasons. Had the court decided in favor of the plaintiffs, the largest class action suit in history could have cost the world's biggest retailer tens of billion of dollars in back pay and punitive damages.