Almost 50,000 U.S. 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.

Demonstrators holds signs during a United Auto Workers (UAW) strike outside the General Motors Co. Flint Assembly plant in Flint, Michigan, U.S., on Monday, Sept. 16, 2019. (Photo: VCG)

Workers from 31 plants opted to walk out after talks between the company and the United Auto Workers (UAW) 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 said. He added 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.

On Wall Street, GM shares fell 4.3 percent. CNBC said the strike could cost the automaker 90 million U.S. dollars 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.

U.S. 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.

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

U.S. 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.