Flint (United States) (AFP) - Almost 50,000 US auto workers went on strike on Monday in a pay dispute with General Motors, the largest industrial action to hit the carmaker in more than a decade.

Workers from 31 plants opted to walk out after talks between the company and the United Auto Workers Union hit an impasse as they tried to negotiate a replacement agreement when the manufacturer's four-year contract with workers expired.

How long the labor action might last was uncertain.

"The strike can take a little while longer," Brian Rothenberg, a spokesman for the powerful union, told AFP. He said that only two percent of issues under negotiation had been agreed upon.

"We have to find common ground on 98 percent of the remaining issues," he said, after the strike began at midnight Sunday, with placard-waving strikers forming picket lines outside assembly plants.

Talks were due to resume later in the morning, UAW officials said.

Car production at the Detroit giant, which was saved by a multi-billion dollar bailout from the Obama administration after the 2008 economic crash, was brought to a complete standstill on Monday, Rothenberg said.

On Wall Street, GM shares fell 4.3 percent. CNBC said the strike could cost the automaker $90 million a day.

"This is our last resort," Terry Dittes, the union's lead negotiator with GM, told a news conference after the meeting Sunday. "We are standing up for the fundamental rights of working people in this country."

UAW officials said the two sides remained far apart on wages, health care benefits, the status of temporary workers and job security.

"Our members have spoken; we have taken action; and this is a decision we did not make lightly," Ted Krumm, chair of the UAW's national bargaining committee, said in a statement.

"We are standing up for what is right," Krumm said.

US President Donald Trump on Monday exhorted both sides to reach a deal and also told reporters he opposed GM plans to shutter US factories or invest outside the United States.

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"I'm sad to see the strike. Hopefully it's going to be a quick one," he said.

Democratic presidential hopefuls also took to Twitter, voicing support for the strike.

"A job is about a lot more than a paycheck. It's about dignity and respect," frontrunner Joe Biden wrote.

Bernie Sanders urged GM to "end the greed."

"Sit down with the UAW and work out an agreement that treats your workers with the respect and dignity they deserve," the Vermont senator tweeted.

GM's last major strike, according to The Wall Street Journal, was in 2007 when 73,000 workers at more than 89 facilities walked off the job for two days.

In a statement, GM said it was "disappointing" that the UAW's leadership had decided to call the strike, saying it had presented a "strong offer" in contract negotiations.

"We have negotiated in good faith and with a sense of urgency. Our goal remains to build a strong future for our employees and our business," it said.

UAW's leadership had previously won overwhelming approval from its rank-and-file for a strike if it became necessary.

- Strong sales, unclear outlook -

Workers at Ford and Fiat Chrysler agreed to extend their contracts, but GM management was informed Saturday that the union would not extend its contract.

Earlier on Sunday, contract maintenance workers walked off the job at GM plants in Michigan and Ohio in a parallel dispute with contractor Aramark.

GM has enjoyed several years of strong sales, posting $11.8 billion in operating profits last year, prompting union officials to argue it is time to share the wealth with workers who have borne the brunt of downturns.

But the outlook for GM is less clear, with concerns growing that a recession may be in the offing amid protracted trade tensions.

GM announced last November it was effectively shuttering five plants in North America, including facilities in Michigan and Ohio that were "unallocated" for production.

Protecting jobs and saving those plants have been key issues in the negotiations.

In its response to the strike, GM's management revealed that its offer included a promise of $7 billion in investments that would save or protect 5,400 union jobs and address the issue of the two "unallocated" plants.

It also promised that a new all-electric truck would be built in a US plant.

Adding to the friction is a federal corruption probe of the union leadership, which resulted in an FBI search last month of the home of UAW President Gary Jones.

A member of the UAW's executive board, Vance Pearson, was arrested on Thursday on charges of conspiracy to use union dues for lavish personal expenses.

Pearson, a UAW director in St. Louis, Missouri, was accused of using union conferences as a cover to justify long-term stays at luxury resorts in California.

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