Workers at Chile''s Escondida Mine, the world''s biggest privately owned copper mine, began a 24-hour "warning" strike Monday over working conditions. The 2,000 employees who skipped work vowed a second day of strikes Wednesday and refused to rule out further action if an agreement over hours and work safety is not begun. "The union called a 24-hour warning strike, and because of this performance was crippled," Gustavo Tapia, president of the Mining Federation of Chile, told AFP.