The progressive group Not One Penny estimated GM's savings from the tax plan total more than $500 million.
Employees were called to report to the plant Monday morning, sources said.
General Motors' decision to halt production in two states that were key to Donald Trump's 2016 victory could complicate the president's re-election bid.
Plants without products include assembly plants in Detroit; Lordstown, Ohio; and Oshawa, Ontario. Automotive News reports that two additional plants - a pair of propulsion plants in MI and Maryland - will also grind to a halt by the end of 2019. Most of the affected factories build cars that won't be sold in the United States after next year.
Brown, a longtime labor union ally, said in a statement that "the company reaped a massive tax break from last year's GOP tax bill and failed to invest that money in American jobs".
GM announced on Monday that it plans to end Lordstown Cruze production in March, saying it has not allocated a new product for the plant. The plants made sedans that have waned in popularity, including the Chevrolet Volt, Impala and Cruise, the Buick LaCrosse, and the Cadillac CT6 and XTS.
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However, such future-minded and proactive thinking is a high-risk, potentially high-reward bet.
GM's (GM) new motto is "Zero Crashes, Zero Emissions, Zero Congestion", signaling a shift to self-driving, electric vehicles. But the operations remain unprofitable.
The company expects to gain 75 percent of its sales from only "five vehicle architectures" by "early the next decade", the news release states. "I've never seen anything like it", Dittes said.
As part of the announcement, G-M said it's scrapping several vehicle models including the Chevy Impala and the Chevy Volt. She later told analysts that the company is "committed to working with GM's unions", however it will be a balancing act for GM to not overplay its hand.
About 6,000 factory workers could lose jobs in the USA and Canada, although some could transfer to truck plants.
The decision by General Motors to cut workers and idle plants is drawing criticism from both the president and the prime minister of Canada.
In GM's third-quarter earnings call with investors, CEO Barra said the decline in sales was not a direct result of tariffs.
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"These are real stakes in front of the bargaining team next year for the negotiations", she said.
With US vehicle sales lagging, several auto plants have fallen to just one shift, including its Hamtramck and Lordstown assembly plants.
GM will also close two additional plants outside of North America by next year. That has not occurred; however, it is expected. GM also plans to close an assembly plant and a transmission plant in OH, along with an assembly plant in Canada.
Some 8,000 salaried employees and 6,000 hourly workers will either lose their jobs or be reassigned to other plants, and more layoffs are likely on the horizon, industry experts said.
The president said that the layoffs had nothing to do with tariffs and instead blamed Barra for making cars that don't sell.
But doing so also leaves automakers vulnerable to shifts in consumer preference back to passenger cars. When, not if, a recession hits - and we're about due - it'll be hard politically for the company to justify layoffs.
"It's not about jobs to them; it's about profits", said U.S. Rep. Timothy J. Ryan, D-Howland. The charges will take place in the fourth quarter of 2018 and the first quarter of next year.
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Almost 21,000 candidates were vying for 11,000 elected positions, from mayors to city councillors and township chiefs. Taiwan's Investigation Bureau is probing Chinese influence on the elections through campaign funding of candidates.
Barra said the move leaves GM to focus on the future.