The United Auto Workers union announced it would begin striking at additional plants if no serious progress was made by Friday in negotiations with automakers Ford, General Motors and Chrysler's parent company Stellantis.
The UAW launched a targeted strike over pay last week against the three automakers, targeting one U.S. assembly plant at each company.
"We're not going to keep waiting around forever while they drag this out. We're not messing around," UAW President Shawn Fain said in a video message on Monday, setting the new deadline after complaining about lack of progress in recent talks.
The union and companies are at odds over pay and benefits for workers. The three automakers have proposed 20% raises over the 4 1/2-year term of their proposed deals, which is half of what the UAW is demanding through 2027. At one point during talks, the UAW offered to lower its demand to 36%.
The UAW is also demanding shorter 32-hour work weeks with pay for the full 40 hours, restoration of defined benefit pensions and stronger job security as automakers move to electric vehicles.
Ford also faces a total strike at its smaller Canadian operations if no agreement is reached soon with the union, which represents about 5,600 Canadian autoworkers – just days after workers at one of the company's U.S. plants walked out.
Canadian union Unifor, whose contract with Ford expired at midnight, said there was still no deal in place.
Unifor National President Lana Payne said in a video posted on the union's website that Ford must do more to meet the union's demands.
"If there is a strike, this will be a total strike," she said. "Every single one of Unifor's 5,600 members at Ford in Canada will be on picket lines."
Ford has two engine plants in Canada that build V-8 motors for F-series and Super Duty pickups assembled in the U.S., and the company also has an assembly plant in Ontario. A walkout by Canadian workers that shut down those engine plants could further damage U.S. production of Ford's most profitable vehicles, even if the UAW elects not to stage walkouts at truck plants in Kentucky; Dearborn, Michigan; and Kansas City, Missouri.
"Ours is a small but highly consequential footprint for Ford operations in North America and this is our leverage, and we will use it," Payne said.
Negotiations between the UAW and the automakers continued on Monday as the strike entered its fourth day. Roughly 12,700 workers are striking at the three U.S. plants, including 3,300 at Ford's assembly plant in Wayne, Michigan.
Union negotiators and representatives of the automakers held talks over the weekend in an effort to end the labor strikes. The UAW held talks with Stellantis over the weekend, but no deal was reached. The union had scheduled a new round of talks with Ford for Monday afternoon.
Fain told NPR on Monday there were "minimal conversations over the weekend, so the ball is in their court," adding that they "have a long way to go."
The strikes have stopped production at plants in Michigan, Ohio and Missouri that manufacture popular vehicle models, including the Ford Bronco, Jeep Wrangler and Chevrolet Colorado.
On Friday, Ford furloughed 600 workers who are not on strike at the Michigan Bronco plant because of the impact of the strike. GM said it expected to halt operations at its Kansas auto plant early this week because of the strike at its nearby Missouri plant, affecting 2,000 workers.
Former President Donald Trump is planning to deliver a speech in Detroit to autoworkers on Sept. 27.
Reuters contributed to this report.