Federal and state laws bar employers from making hourly employees work unpaid hours. Wal-Mart's policies forbid such work. But many current and former workers and managers said an intense focus on cost cutting had created an unofficial policy that encouraged managers to request or require off-the-clock work and avoid paying overtime. Accusations like these are at the heart of a wide-ranging legal battle between Wal-Mart and employees or former employees in 28 states.