OTTAWA--Canada's union representing auto-assembly workers demanded on Wednesday that the federal government block Stellantis's plan to sell its idled Toronto-area factory to a local defense firm, arguing that the carmaker is trying to violate its commitment to employees and taxpayers.

Lana Payne, the president of Unifor, also asked Canadian Industry Minister Melanie Joly in a letter to disclose any role federal officials had in talks between Stellantis and armored-car producer Roshel, and whether transferring the plant in Brampton, Ontario to the defense company would address government concerns.

"We cannot accept that the closure and sale of the Brampton plant is the outcome of a year-long government-led exercise to protect autoworkers and auto capacity in this country," Payne said in the letter, which was distributed to journalists. "The Stellantis proposal to sell the plant to a non-automaker never should have been considered in the first place and should be met with fierce resistance from the federal government."

The union declared labor negotiations with Stellantis at an impasse due to the car maker's intention to sell the plant to Roshel. The automaker and the defense firm have signed a so-called memorandum of understanding to advance negotiations toward a sale. The current Unifor-Stellantis labor deal expires on Sept. 20, raising the specter of a strike by unionized workers.

A spokeswoman for Joly wasn't immediately available for comment. Government officials have been in talks with the company about the future of the Brampton plant, and Joly had previously threatened to sue Stellantis for failing to meet employment and production commitments after the company received taxpayer-backed financing to retool factories.

A spokesman for Canada's Department of Industry said last week any sale of the plant would need to comply with commitments Stellantis has made, adding it was "aware" of reports regarding a Stellantis-Roshel transaction. Canada's registry of lobbying activity indicates meetings in August between representatives for Roshel and industry department officials.

Payne, in her letter, also asks Joly to disclose what discussions her officials had with Roshel, and whether the government would back the plant sale. "The idea Canada would concede defeat on one of its remaining vehicle assembly plants is unfathomable," Payne said.

A Stellantis spokeswoman was not immediately available for comment. Stellantis said last week a sale to Roshel would help restore manufacturing operations in Brampton. The carmaker was slated to produce its Jeep Compass at the Brampton plant following a retooling. But last year--under pressure from U.S. tariffs--Stellantis said it would transfer the production to Illinois, with U.S. automakers under pressure from hefty Trump administration tariffs.

A Roshel spokesman said it is willing to make employment commitments to affected Stellantis employees as part of the transaction.