United Auto Workers members picket outside the General Motors Detroit-Hamtramck assembly plant in Hamtramck, Mich., Monday, Sept. 16, 2019. Roughly 49,000 workers at General Motors plants in the U.S. went on strike just before midnight Sunday, but talks between the UAW and the automaker will resume. (AP Photo/Paul Sancya)

DETROIT (AP) — More than 49,000 members of the United Auto Workers walked off General Motors factory floors or set up picket lines early today as contract talks with the company deteriorated into a strike.

Workers shut down 33 manufacturing plants in nine states across the U.S., as well as 22 parts distribution warehouses.

It wasn’t clear how long the walkout would last, with the union saying GM has budged little in months of talks while GM said it made substantial offers including higher wages and factory investments.

It’s the first national strike by the union since a two-day walkout in 2007 that had little impact on the company.

GM workers joined striking Aramark-employed janitors assigned to GM facilities on the picket lines Sunday night at a sprawling factory on the border between Detroit and the small town of Hamtramck.

Worker Patty Thomas said she wasn’t scheduled to picket, but came out to support her colleagues at the car plant, which GM wants to close.

She’s heard talk that GM may keep the factory open and start building electric pickup trucks there, but she’s skeptical.

“What are they going to take away?” she asked. “That’s the big issue.”

She said workers gave up cost-of-living pay raises to help GM get through bankruptcy, and workers want some of that back now that the company is making profits.

Striking GM employees were joined on the picket lines by workers from Ford and Fiat Chrysler, who are working under contract extensions.

Night shift workers at an aluminum castings factory in Bedford, Indiana, that makes transmission casings and other parts shut off their machines and headed for the exits, said Dave Green, a worker who transferred from the now-shuttered GM small-car factory in Lordstown, Ohio.

Green, a former local union president, said he agrees with the strike over wages, plant closures and other issues.

“If we don’t fight now, when are we going to fight?” he asked. “This is not about us. It’s about the future.”

UAW Vice President Terry Dittes, the union’s top GM negotiator, said a strike is the union’s last resort but is needed because both sides are far apart in negotiating a new four-year contract. The union, he said Saturday, does not take a strike lightly.

“We clearly understand the hardship that it may cause,” he said. “We are standing up for fair wages, we are standing up for affordable quality health care, we are standing up for our share of the profits.”

GM, however, said it offered pay raises and $7 billion worth of U.S. factory investments resulting in 5,400 new positions, a minority of which would be filled by existing employees. GM would not give a precise number. The company also said it offered higher profit sharing, “nationally leading” health benefits and an $8,000 payment to each worker upon ratification.

Because public statements from both sides conflict, it’s hard to tell how long the strike will last, said Kristin Dziczek, vice president of labor and industry at the Center for Automotive Research, an industry think tank.

The length “depends on how far apart they really are and where the lines in the sand are drawn,” she said.

Talks were scheduled to resume at 10 a.m. EDT today.

The union’s contract with GM expired Saturday night, but pacts with the company’s crosstown rivals, Ford and Fiat Chrysler, were extended indefinitely. The union has picked GM as its target company this year, and any deal it negotiates will be used as a template for the others.