Autoworkers at General Motors Corp.'s truck plant in Oshawa, Ont., were dealt another blow Monday when the company said it will periodically be shut down beginning next month.

The temporary layoffs will begin in July after a two-week annual shutdown to adjust operations for the model-year changeover, the company said.

After that, seven more weeks of down time will occur at unspecified points between July and the end of the year, GM spokeswoman Patty Faith said. It will affect about 1,000 workers, she said.

Canadian Auto Workers union president Buzz Hargrove said Oshawa is scheduled to resume regular production in January and the temporary closure was considered "additional time off which will be covered by EI [unemployment insurance]."

He added that GM still plans to close the Oshawa plant in the fall of 2009, though the union intends to "try and find every way we can to change their mind or stop them."

Industry watcher Dennis DesRosiers said the latest GM announcement was purely market-driven, and didn't surprise him.

He noted that GM truck production has declined 70 per cent this year in Canada, while it's down 40 per cent in the United States.

"I don't think General Motors is trying to play to anybody here, I think they're playing to one thing only — and that's the market. They're not playing politics here," he said.

Earlier Monday, the CAW issued new data which claims that during the first four months of the year Canada's auto trade deficit almost doubled to $3.7 billion, caused by a "sharp decline" in auto exports to the U.S., and higher imports from overseas.

Exports of finished vehicles dropped 25 per cent, the report said.

The union estimated that Canada's auto trade deficit could climb to more than $10 billion if the current trend holds. Last year the deficit was just $6.6 billion.

Hargrove has been pushing Ottawa to regulate automotive imports and make arrangements with foreign governments to import Canadian parts and vehicles. He said those actions would help turn around the struggling industry.