Four weeks after starting limited strikes against three large automakers, the United Automobile Workers is shifting to a more aggressive strategy, suggesting that work stoppages could spread to more plants and possibly go on for some time.
In an online video, the union’s president, Shawn Fain, said on Friday that he would no longer wait to announce expansions of the strikes on Friday, as he had been doing. Further actions could come at any time.
“We’re not messing around,” Mr. Fain said. “The companies are now on notice. If they’re not willing to move, we are going to give them a push.”
The union began its strikes on Sept. 15 when workers walked out of three plants, owned by General Motors, Ford Motor and Stellantis, which makes Chrysler, Jeep and Ram vehicles. It has since expanded the strike in stages, in a bid to increase the pressure on the companies.
Stellantis said on Friday that it was temporarily laying off an additional 700 workers at two plants in Indiana that supply transmissions and castings for a Toledo, Ohio, Jeep factory that has been idled by the U.A.W. strikes. Stellantis has laid off more than 1,300 workers in total in response to the union’s strikes.
Ford has laid off more than 1,900 workers as a result of the strike, and G.M. about 2,300. Ford said about 90 of its parts suppliers had laid off about 13,000 workers.
Stellantis also said its negotiations had made progress in talks with the U.A.W. this week. The company said it hoped “to reach an agreement as soon as possible to get everyone back to work.”
The U.A.W. and the automakers have been negotiating new labor contracts since July.
On Wednesday, the U.A.W. unexpectedly told workers to walk out of Ford’s Kentucky Truck Plant in Louisville. It is the company’s largest and the producer of its highly profitable Super Duty version of its F-Series pickup trucks.
Ford has said the Kentucky plant typically produces a new truck every 37 seconds, and generates $25 billion in revenue, about 16 percent of the company’s annual total.
All told, the strike has halted operations at three Ford plants in Michigan, Chicago and Kentucky; two G.M. plants in Michigan and Missouri; and a Stellantis plant in Ohio. U.A.W. members are also on strike at 38 G.M. and Stellantis spare-parts warehouses across the country.
About 34,000 of the 150,000 U.A.W. members employed by the three companies are now on strike.
The U.A.W. has demanded substantial wage increases and improvements in other areas of its contract, like retirement plans. The union also wants an end to a system that pays new hires a little over half the top U.A.W. wage of $32 an hour.
The union is also concerned about the possible loss of jobs as automakers ramp up production of electric vehicles. The companies have offered wage increases of more than 20 percent over four years and to reduce the time it takes a new worker to rise to the top wage to four years from eight.
On Thursday, Ford officials said the company had reached its limit on what it could offer the union without hurting the company’s business and its ability to continue heavy investments in electric vehicles. “Any more will stretch our ability to invest in the business,” Kumar Galhotra, president of the Ford division that makes combustion engine vehicles, said on a conference call on Thursday.
Apart from the car companies, U.A.W.-represented workers went on strike this week at Mack Trucks. Its members voted this week to authorize a strike against General Dynamics, an aerospace and defense contractor. The U.A.W. also represents about 1,000 workers who have been on strike at Blue Cross Blue Shield of Michigan for a month.