Tens of thousands of auto workers across the country went on strike Sunday night after negotiations faltered between their union and General Motors.

The strike began at 11:59 p.m. ET., with as many as 50,000 United Auto Workers at dozens of facilities from Michigan to Texas expected to participate.

Union spokesman Brian Rothenberg told The Associated Press on Sunday night that negotiations would resume on Monday morning, even as the strike went forward.

In a letter to members on Saturday night, the union’s vice president, Terry Dittes, said that negotiators still hadn’t been able to agree on wages, health care benefits, temporary workers, job security and profit sharing.

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During a press briefing on Sunday morning, Dittes called the decision to strike a “last resort.”

"This is about standing up for us, the families and the communities that are affected because this is not just about our members. This is about a bigger picture," Dittes told NBC News Monday morning.

While the company has an obligation to structure its business the way it sees fit, Dittes said. "We have an obligation to represent our members," he added. "Now is our time."

General Motors called the walk-off “disappointing,” saying in a statement that it put forward a "fair offer" that included “best in class wages” and “nationally leading health care benefits.”

Roughly 200 local union leaders voted unanimously to support the strike, Rothenberg said earlier.

The move could cost hundreds of millions of dollars. A two-day strike in 2007 — the last time the UAW called such a work stoppage — cost General Motors more than $600 million.

UAW member Steve Harrod has worked for GM for 20 years and told NBC News over the phone that he is hopeful that the union will secure most of its demands.

"I think we won’t get everything we want but I think it'll be decent. We’ll be OK," said Harrod, who works on an assembly line in Lansing, Michigan, making the Buick Enclave and Chevrolet Traverse.

He would like to see General Motors commit to keeping production in the U.S. and the hiring of temporary workers, many who have been at his plant for years, he said.

"Hopefully it doesn’t last longer than a week or two but if it does, it does," he added.

Dittes echoed Harrod on the status of temporary workers. Employees previously went from temporary workers to full-time status in a short amount of time, Dittes said, who has been at the company for decades. Now, people will spend four years as a temporary employee, with what Dittes described as "substandard pay" and "different benefits."

Dorrit Madison of Flint, Mich., demonstrates outside the Flint Assembly Plant on Sunday. A two-day strike in 2007 cost GM more than $600 million. Jake May / AP

President Donald Trump encouraged the two sides to continue negotiating, saying in a tweet: "Here we go again with General Motors and the United Auto Workers. Get together and make a deal!"

Democratic presidential hopefuls meanwhile, tweeted messages of support for the striking workers.

"@GM should do right by the workers who fuel its profits," tweeted Mayor Pete Buttigieg of South Bend, Indiana.

Former Vice President Joe Biden, former Housing Secretary Julián Castro, Sens. Elizabeth Warren, D-Mass., Bernie Sanders, I-Vt., and Kamala Harris, D-Calif., also backed the workers in tweets.

The strike comes weeks after federal authorities reportedly raided the home of UAW president Gary Jones. The raid appeared to be part of a corruption probe that included the arrest on Thursday of Vance Pearson, a member of the union’s international executive board, on charges of embezzlement.