The union told 5,000 workers to step down at the plant, General Motors’ largest in the United States, as it escalates its labor action at the three large U.S. automakers.
The three U.S. automakers say they are already at a disadvantage to nonunion rivals while labor leaders hope that big gains in negotiations will inspire workers in Southern states to unionize.
Mr. Ford, the executive chairman of Ford Motor, said nonunion automakers would make gains against Michigan automakers because of strikes by the United Automobile Workers union.