The United Auto Workers said it will expand its strikes at the legacy Detroit automakers at noon on Friday if “serious progress” isn’t made in negotiations.

“Either the Big Three get down to business and work with us to make progress in negotiations, or more locals will be called on to stand up and go out on strike,” UAW President Shawn Fain said in a video posted on Facebook.

A union representative said earlier that no new offers had come from General Motors Co., Ford Motor Co. or Stellantis NV since the union made its proposals on Sept. 14, right before its strike against the automakers began.

A bargaining update issued Sept. 16 by Stellantis, maker of Jeep and Chrysler models, was described in some media reports as a new offer. But the latest proposal on the table was made by the UAW, according to a person familiar with the contract talks, who asked not to be identified revealing internal discussions.

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Stellantis said Monday in an emailed statement that it resumed negotiations and had a “constructive” discussion with union representatives focused on “common ground.” It said it was offering nearly 21% in pay raises and was committed to finding a solution for its idled Belvidere, Illinois, Jeep plant.

Over the weekend, the company’s top negotiator said the Belvidere plant proposal was no longer on the table after the UAW rejected its last offer before the strike deadline.

On Sunday, Fain rejected the Stellantis 21% pay increase offer as a “no-go.”

Citing unnamed sources, CNBC reported that Stellantis’s proposal could lead to the closure of 18 facilities, including parts and distribution centers. The automaker’s North American headquarters and technology center in Detroit could also be affected, it said.

The UAW strikes began Sept. 15, minutes after contracts with the carmakers expired. Nearly 13,000 workers walked off jobs at a Ford plant in Michigan making Bronco SUVs, a GM factory in Missouri that assembles Chevrolet Colorado pickups and a Stellantis plant in Ohio that builds Jeep Wrangler SUVs.

GM and Ford have announced layoffs of non-striking workers, citing what they’ve described as spillover effects of the three-factory walkouts. The UAW will pay those workers the equivalent of $500 a week in strike pay, even though they are not on strike, the person said. The union has about $825 million in its strike fund.

The UAW has declined to detail its latest offer, but the companies have said the union lowered its demand for a pay raise to 36% from 40%. GM and Ford have each countered with offers of a 20% raise, which the union rejected. The latest offer from Stellantis is for a 19.5% raise, which increases to 21% when it is compounded over the life of the deal, the person said.

The union conducted negotiations with Ford on Sept. 16, characterizing them as “reasonably productive.” It had talks with GM Sunday and confirmed talks with Stellantis on Monday, but didn’t say how those discussions went.

--With assistance from Eduard Gismatullin.

(Updates with Friday deadline for expanded strikes.)