Nemak is turning to the Ontario Labour Relations Board to stop a blockade in Windsor by Unifor.
Workers walked off the job Monday morning and are not allowing anything in or out of the plant until the company reverses its decision to shut down.
The aluminum casting plant is scheduled to close in mid 2020, putting 270 people out of work but the contract signed between the company and union indicated the plant would remain open until 2022.
The decision to close the plant was based on GM in China deciding to in source its engine block.