A top UAW official told striking General Motors workers Thursday afternoon that "some progress has been made" in contract talks, but many issues remained unresolved. Meanwhile, the strike began to cause layoffs among suppliers.

Terry Dittes, vice president of the UAW's GM Department, said in a letter that talks would continue "this weekend and beyond" if no agreement is reached sooner.

Negotiating teams have worked into the evening each day since the strike started at 12:01 a.m. Monday.

Bargainers are mum on the precise sticking points, one union local leader said. Dittes' letter said talks were under way "in subcommittees and main tables."

As the strike reached its fourth day, rumors grew among strikers, including one that GM was hiring temporary workers at Arlington Assembly plant in Texas. Striking workers in several locations around the country said they had been told GM was paying strike-breakers $12 an hour to cross the picket lines and start building full-size SUVs.

A GM spokesman said that was "absolutely false." The UAW in Detroit also said it had debunked the rumor.

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Some suppliers were laying off employees for lack of work. A GM spokeswoman said local GM plants were not accepting deliveries due to the strike.

Nexteer Automotive, a supplier of steering and driveline components, said it "faced the difficult conclusion to temporarily reduce our workforce in the coming days due to the disruption in GM production," according to a statement from Dennis Hoeg, North America Division President of Nexteer.

Automotive Component Carrier, a delivery service that GM uses for its facilities in Flint and Saginaw, laid off 107 drivers Monday, said Randy Ryerson, director of communications for Penske Logistics which owns ACC.

ACC delivers automotive components to GM’s factories. GM has three factories in Flint: Flint Assembly, Flint Engine Operations and Flint Metal Center. GM also has Saginaw Metal Casting Operations.

The drivers will be off for the duration of the strike, said Ryerson.

“When the factories aren’t working, we’re not working,” said Ryerson, adding: “The drivers are unionized, so they would not cross the line.”

Lear Seating and Universal Delivery were said to have temporarily laid off hundreds of workers, according to Flint's local UAW chief.

A representative who answered the phone for Universal Delivery in Flint, a delivery and logistics company, said, “We’re definitely down. When the assembly plant is down, we’re down.” She confirmed workers were temporarily laid off, but declined to say how many or give her name.

A spokeswoman for Lear Seating declined to comment.

According to an August 2018 press release, Lear, which is a global supplier of car seating and electrical systems, opened a 156,000-square foot facility in Flint that would employ about 600 people. The release said, “This facility will build seats for just-in-time delivery to the nearby General Motors Flint Assembly plant as well as the General Motors Fort Wayne plant in Indiana.”

GM builds the heavy-duty Chevrolet Silverado and GMC Sierra crew and regular cab pickups at Flint. At Fort Wayne, GM builds the GMC Sierra 1500 and Chevrolet Silverado 1500 pickups.

Across the street from GM's Fort Wayne, Indiana, plant, supplier Avancez stopped operations shortly after the strike began, NPR reported. Some 300 Avancez workers install wiring and dome lights into headliners for various GM vehicles.

The Lansing State Journal reported that Todd Collins, president of UAW Local 724, said businesses that supply parts to Lansing's GM plants had temporarily laid off workers as of Monday. Those include Bridgewater Interiors, Alliance Interiors and Dakkota Integrated Systems. Representatives of those companies did not return requests for comment, the State Journal said.

The strike is the first by the UAW since 2007, just before the Detroit auto companies and the national economy nose-dived into the Great Recession. The union struck GM for two days then and, later, Chrysler for six hours. In the coming years, auto manufacturing employment plummeted, and many of today's autoworkers have known only years of strong profit.

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What's known of key points in the discussions:

Health care: GM initially proposed that workers pay 15% of their costs, up from their current 3%, but reportedly has backed off. Workers are adamant they need to maintain their coverage, which is far less expensive to them than to almost all other American workers. GM, which spends $1 billion a year on health care, did kick responsibility for those costs during the strike to the UAW strike fund, sparking sharp bickering between the two sides.

Wages: Workers, whose pay has regressed 16% against inflation since 2010, say it's their turn to be rewarded after years of profits for GM and the other automakers. They also want to equalize pay for workers hired after 2007, who start at $17 per hour and can rise to about $28 per hour after seven years. GM initially offered 2% raises and 2% lump sums in alternating years of the next four-year deal.

Temporary workers: About 7% of GM's workforce over the course of a year is temporary workers, who are paid $15 an hour and lack the opportunity to transfer if their plant closes. The union wants a path for them to become permanent; GM wants the right to hire more temps for flexibility.

Job security: GM has offered $7 billion in investment and said it would keep or retain 5,400 jobs over the life of the contract.

The union chose to negotiate first with GM in an effort to reach a template agreement that it can then take to Ford and Fiat Chrysler Automobiles, which are operating under contract extensions.

More:GM promises UAW 5,400 jobs, $7B in US investment: What it means

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Contact Jamie L. LaReau at 313-222-2149 or jlareau@freepress.com. Follow her on Twitter @jlareauan. Read more on General Motors and sign up for our autos newsletter. Phoebe Wall Howard contributed to this article.