General Motors Co. is planning to use the Oshawa Assembly Plant in Ontario for additional production of the Chevrolet Silverado and GMC Sierra pickups, a move which the Unifor Local 222 union believes will lead to hiring about 500 workers.

The Unifor Local 222 Canadian auto union, on its website, said truck work is coming to the plant early next year. It marks a return of truck production to Oshawa after nearly a decade.

GM would not comment directly on the truck work or the possible jobs addition at the Oshawa plant. “Work is well underway at Oshawa Assembly on investments taking place in the plant to support exciting new model and product changes,” the automaker said in a statement Tuesday.

The new work is part of a four-year agreement reached last fall between Unifor and GM. GM is expected to spend about CA$400 million to upgrade the flex line inside the Oshawa plant.

Last fall, Unifor President Jerry Dias said the Oshawa plant would be the first in North America capable of building both cars and trucks. Some GM pickup volume is expected to move from its Fort Wayne Assembly Plant in Roanoke, Indiana, as vehicle bodies will be sent from Indiana to Oshawa for final assembly, according to a source familiar with the company’s planning who asked not to be identified because the details have not been made public.

The Oshawa plant currently builds the Chevrolet Equinox on its consolidated line, which is expected to end production this summer. About 600 employees now work on that line and some may be temporarily laid off, according to the union. A flex line builds the Buick Regal, Cadillac XTS and Chevrolet Impala. The Regal is expected to end production at the plant in the fall.

Unifor Local 222 is asking Oshawa hourly workers if they would elect to retire between Aug. 1 and Jan. 1; to work in the truck area but go on layoff after the consolidated plant ceases production until November or December; or to work on the flex line, depending on seniority. The truck production is expected to begin in January, according to Unifor.

“We are confident no full-time members will be affected following the results of the retirement canvass, plus the fact we presently have open jobs in both plants…,” Unifor Local 222 said in a posting on the website. “The second shift in truck will be launched in the second quarter of 2018 by the shutdown period. At this time it is forecast that another 500 jobs will be added to truck.”

The Oshawa plant has about 2,400 employees, down significantly from the more than 10,000 the facility employed a decade ago. GM shuttered the Oshawa Truck plant in 2009 due to slowing truck sales amid high gasoline prices and because of the financial crisis and economic downturn.

GM also builds Silverados and Sierras at its Flint Assembly Plant and in Silao, Mexico. The carmaker has billions of dollars of investments planned for its Fort Wayne and Flint plants, likely to ready them for GM’s next-generation pickup trucks which are expected to include more use of aluminum.

The automaker is taking several weeks of downtime this year to begin preparing for next-generation pickup. Some analysts expect to see the redesigned models on the road late next year as 2019 models.

U.S. sales of the Silverado through April totaled 168,621, down 5.8 percent and Sierra sales totaled 67,210, down 6.2 percent.

GM Chief Financial Officer Chuck Stevens told reporters in Detroit last month that the company remains bullish on the U.S. pickup market.

GM’s full-size SUV plant and three truck plants are running three shifts to meet demand, he said. GM sees growth for profitable trucks as there is replacement demand given the average age of pickups on the road in the U.S. is about 14 years vs. the about 11.5 years for all vehicles, Stevens said. Expected low gas prices continuing and likely U.S. economic growth also will aid growth, he said.

“If we do see the kind of economic growth infrastructure spending that has been put forth by the Trump administration, that will lead to construction, which leads to further demand for trucks,” Stevens told reporters. “So we’re quite optimistic that the truck market’s going to continue to be strong.”

mburden@detroitnews.com