DETROIT (AP) — Contract talks between the United Auto Workers and General Motors showed some signs of progress as a strike by more than 49,000 employees extended into a second day.

The walkout brought to a standstill more than 50 factories and parts warehouses in the union's first strike against the No. 1 U.S. automaker in over a decade. Workers left factories and formed picket lines shortly after midnight Monday in the dispute over a new four-year contract.

"They are talking, they've made progress, we'll see how long it takes," Brian Rothenberg, spokesman for the UAW, said Tuesday.

One of the main sticking points is health care. GM is looking to cut its costs, but workers say they shouldn't have to pay more because the company is making billions in profits. Union workers pay about 4% of their health care costs, but employees of large companies in the U.S. pay an average of 34%, according to the Kaiser Family Foundation.

Tina Black, who finishes up 10-speed automatic transmissions at a GM engine and transmission factory in the Detroit suburb of Romulus, said health insurance is the most important issue to her, and she doesn't want GM to change anything.

The factory workers, she said, work 10-12 hours doing the same repetitive tasks, which can cause injuries.

"It breaks down your body," said Black, of Garden City, Michigan. "In order to take care of ourselves, we need that."

There are still many other important items left in the talks, including wage increases, pay for new hires, job security, profit sharing and treatment of temporary workers, said UAW Vice President Terry Dittes in a letter to GM Sunday. But even with those issues unresolved, Dittes said that the strike could have been averted had the company made its latest offer sooner.

On Sunday, GM 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. The company also said it offered higher profit sharing, "nationally leading" health benefits and an $8,000 payment to each worker upon ratification.

In addition, GM pledged to build a new all-electric pickup truck at a factory in Detroit and open an electric vehicle battery plant in Lordstown, Ohio, according to a person who spoke to The Associated Press on condition of anonymity. The person was not authorized to disclose details of the negotiations. The new factory would be in addition to a proposal to make electric vehicles for a company called Workhorse, the person said.

It's unclear how many workers the two plants would employ. The closures, especially of the Ohio plant, have become issues in the 2020 presidential campaign. President Donald Trump has consistently criticized the company and demanded that Lordstown be reopened.

Dittes told GM that those company concessions might have made it possible to reach an agreement if they had come earlier.

"We are disappointed that the company waited until just two hours before the contract expired to make what we regard as its first serious offer," Dittes wrote in the letter to Scott Sandefur, GM's vice president of labor relations.

The letter suggests that the company and union are not as far apart as the rhetoric leading up to the strike had indicated.

Kristin Dziczek, vice president of labor and industry for the Center for Automotive Research, an industry think tank, said the letter and resumption of contract talks are encouraging signs that the strike could be shorter than expected.

The strike shut down 33 manufacturing plants in nine states across the U.S., as well as 22 parts-distribution warehouses. It's the first national strike by the union since a two-day walkout in 2007 that had little impact on the company.

Workers at Fiat Chrysler and Ford continued working under contract extensions. Any agreement reached with GM will serve as a template for talks with the other two companies.

GM shares fell more than 4% Monday, but they recovered slightly to $38.20 on Tuesday afternoon.

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Associated Press Writer John Seewer in Toledo, Ohio, contributed to this report.