The retail giant Wal-Mart has lost an effort to dismiss the largest class-action employment discrimination case in U.S. history. On Tuesday, a federal appeals court upheld a ruling that Wal-Mart face a lawsuit alleging discrimination against female employees. Taking the case to trial could expose Wal-Mart to paying billions in damages. Wal-Mart is lobbying against a class-action suit and wants each case tried individually.