U.S. Labor Secretary Elaine Chao said today investigators from her department's wages and hours division are working with the state to see that back wages are paid to immigrant employees of one of San Francisco's largest garment factories. The immigrants are owed as much as $850,000, having not been paid for four months by Wins of California Inc., which makes clothing for customers that include the U.S. Army and Air Force, Sears, Wal-Mart and Kmart, authorities say.