General Motors' decision to close its Oshawa, Ontario, assembly plant is going to be hard-fought as far as the country's auto union is concerned.

Unifor president, Jerry Dias, is due to meet General Motors executives in Detroit today (8 January) to discuss the closure scheduled for December 2019.

"I have no idea if it's going to be positive or negative," Dias told Reuters in an interview.

"I'm optimistic it will be positive, but I'm not even going to try to guess what they're going to tell us."

After meeting with GM executives in Detroit on 20 December, Dias told Reuters the automaker would respond to the union's proposals by 7 January.

Dias said he did not think chief executive Mary Barra – who has taken heat on Capital Hill for closure of five plants in North America – would be at the Tuesday meeting.

He told Reuters one option would be to extend operations for nine months when regular contract talks are scheduled to begin: "That gives us all time to figure out a long-term solution," he said.

The Oshawa shutdown is part of a broad restructuring announced in November. Including the four US plants, about 15,000 jobs will be axed in North America.

Reuters noted Barra promised in early December to keep an "open mind" about another affected plant, Ohio's Lordstown Assembly.

GM had said closing Oshawa affects 2,973 assembly line jobs. The company employs 8,150 in Canada where it has other plants, R&D and distribution, marketing and sales units.

The automaker has also blamed shifting consumer tastes as buyers abandon conventional passenger cars for crossovers in particular.

A study by just-auto's US analyst, Bill Cawthon, showed passenger cars' share of the US market in 2018 fell 4.66% to 30.92% in calendar 2018. Crossovers/SUVs slice rose 4.02% to 46.55%. Pickup trucks' share was up 0.61% to 16.99%.