By the early 1980s, more than 23,000 workers were employed at GM in Oshawa.
She added that the largest United States automaker is "taking these actions now while the company and economy are strong, to stay ahead of fast-changing industry and market conditions".
The automaker said it would shift resources to investing in electric and autonomous vehicles.
GM also said it will reduce salaried and salaried contract staff by 15 per cent, which includes 25 per cent fewer executives.
The decision was part a global restructuring for the company that also includes winding down production at four USA assembly plants and other cuts to free up US$6 billion for investments in the new initiatives. GM did not say the plants would close - it used the term "unallocated" - but sources tell the Globe and Mail the Oshawa facility will close, eliminating more than 2,500 jobs.
The two MI assembly plants GM announced will close are the Detroit-Hamtramck Assembly Plant and the Warren Transmission Plant.
"This industry is changing very rapidly, when you look at all of the transformative technologies, be it propulsion, autonomous driving..." We want to make sure we're well positioned, Ms. Barra told reporters. Co. reported a US$991 million profit during its third quarter, but said tariffs cost the company about US$1 billion.
"The first thing I said to (the president of GM) 'is there anything we can do as a province, absolutely anything, ' and the answer was no, there's nothing".
The union representing the Oshawa auto workers says it will put up what it calls "the fight of our lives" to keep the plant open and save thousands of jobs.
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Premier Doug Ford is acknowledging a very hard day for GM and its suppliers, after learning of the closure of the Oshawa Assembly Plant. The Cadillac XTS and CT6, the Buick Lacrosse and Chevrolet's Impala, Cruze and Volt no longer will be made, meaning the factories that make them won't be needed.
Production at the plant in Oshawa, Ontario fell to about 148,000 vehicles previous year from a peak of 940,000 in 2003, a drop of about 85 per cent, according to Dennis DesRosiers of DesRosiers Automotive Consultants Inc.
Despite the Oshawa loss, Prencipe said he still has faith in the automotive sector in Canada.
"The impact to GM's total vehicle build is expected to be quite minimal at this point in time meaning we will still be supplying product to the powertrain programs that supply those vehicle platforms at expected volumes", said Linamar CEO Linda Hasenfratz in an emailed statement.
"I don't know how I'm going to feed my family", he said outside of the plant's south gate, where workers instituted a blockade for trucks from the entrance.
While still the economic powerhouse of the city of about 160,000 people 60 kilometres east of Toronto, the GM operations in Oshawa are only a small remnant of the 40,000-worker monolith that once dominated the area's economy.
Production at the plant began on November 7, 1953, and in the 1980s the plant employed roughly 23,000 people.
In 2009, GM shut down truck assembly at the plant, citing high gas prices and a deep recession caused by the financial crisis.
While Wall Street praised the actions as cost-cutting measures that will save the automaker $6 billion by 2020, union and political leaders condemned the moves as shortsighted and a betrayal to its workers and government, which less than a decade ago bailed out the automaker from bankruptcy.