Nearly 50,000 workers in the United Auto Workers union go on strike against General Motors, the largest US automaker.

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New York (CNN Business) - The United Auto Workers union, UAW, went on strike against General Motors on Sunday night, the first work stoppage in the US auto industry in 12 years .

The union's almost 50,000 temporary and full-time workers left 31 General Motors factories and 21 other facilities, spread across nine states, mainly in the center of the country. It is the biggest strike of any union against any company since the last strike at General Motors in 2007.

The strike began at 11:59 pm Sunday night. The two sides did not meet formally on Sunday after the union declared its intention to strike at a press conference in the morning, although union spokesman Brian Rothenberg said the dialogue between the two parties was ongoing. A new meeting of the two parties is scheduled for 10 am Monday.

The union said General Motors was putting the profits above the employees who helped save the company when it declared bankruptcy and needed a federal bailout a decade ago.

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The union looks for higher hourly wages, fixed amount payments and a better benefit plan. He also wants General Motors to agree to limit the use of temporary workers and give them a clearer path to permanent employment. In addition, UAW says that the two sides are far apart on other issues, including health care benefits and job security.

General Motors said it made a substantial offer, which included higher wages and profit sharing, along with investments to generate new jobs. He said he offered to commit to investing 7,000 million dollars in the coming years to preserve 5,400 jobs. He also promised a “solution” for two of the four plants currently scheduled for closure: one in Detroit and one in Lordstown, Ohio.

The company did not say what the solution would be. But a person familiar with the General Motors offer said it included the promise to build a new electric truck in Detroit Hamtramck, and build new batteries for electric vehicles in Lordstown. That work would not start immediately, so the plants would probably remain dark for some time. Work will begin sometime in the next four years if the offer is accepted.

Members of the United Auto Workers union meeting outside the General Motors Detroit-Hamtramck assembly plant in Hamtramck, Michigan, early Monday.

A source close to UAW with direct knowledge of the negotiations said that most of the proposals that the company publicly disclosed on Sunday arrived very late in relation to Saturday's negotiations.

General Motors announced plans in November 2018 to close the Detroit and Lordstown assembly plants, along with the transmission plants in Baltimore and Warren, Michigan.

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UAW has made it clear that keeping plants open is a key negotiation demand. On Saturday night, he said that while there was progress in the talks, there were still "significant differences between the parties in terms of salaries, health care benefits, temporary employees, job security and profit sharing."

General Motors says its average hourly employee earns about $ 90,000 per year, not including benefits. But the number of workers per hour at General Motors has declined dramatically in recent decades, due to a combination of automation, loss of market share and outsourcing. But General Motors still manufactures the overwhelming majority of cars sold in the US market in North America. And it has many more factories in the United States than in Mexico or Canada.

The union had previously extended the contracts to two other US automakers with UAW, Ford and Fiat Chrysler contracts. Any agreement reached with General Motors will establish a pattern for conversations with the other two companies.

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The three automakers are dealing with slower sales and the need to make multi-million dollar investments in the development of electric and autonomous vehicles that have a longer-term potential than current market demand.

It was because of the need to save money for those efforts that General Motors halted operations at three US plants, including the assembly line in Lordstown, and announced plans to close the Hamtramck plant, its last Detroit factory, in the early next year.

But negotiations occur when the union is affected by a scandal involving the misappropriation of union funds and, in some cases, union officials who accept bribes from Fiat Chrysler officials. Nine people associated with the union or with Fiat Chrysler have already pleaded guilty to federal charges.

Last week, Detroit News reported that union president Gary Jones was the union official identified in the most recent indictment as "UAW Officer A." The union has not responded to a request for comment on that report.

Experts say the scandal will make it more difficult to get union members to organize and present to automakers to ratify any tentative agreement reached by union leaders. Four years ago, all agreements passed only by narrow margins, although there was no scandal at that time.

The last strike 12 years ago lasted only three days, but some strikes against General Motors in the past have lasted for months. For many of the employees hired since 2007, this is their first work stoppage.

CNN's Scott McLean contributed to this report.

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