The United Automobile Workers union said late Thursday that its members were set to walk off the production lines in three plants in three states at midnight in what would be the first strike simultaneously affecting all three Detroit automakers.
The union and the companies — General Motors, Ford Motor and Stellantis, the parent of Chrysler — remained deadlocked in negotiations over a new collective bargaining agreement with the current contract set to expire at 11:59 p.m.
At the outset, the strike would idle one plant owned at each automaker, and could force the automakers to halt production at other locations, shaking local economies in factory towns across the Midwest.
“We are using a new strategy,” the union’s president, Shawn Fain, said in a video streamed via Facebook. “We are calling on select locals to stand up and go out on strike.”
In the 88 years since it was founded, the union has called strikes aimed at a single automaker, and a handful have halted production for several weeks. G.M. plants were idle for 40 days in 2019 before the company and the union agreed on a new contract.
The plants designated for walkouts on Friday represent only a small portion of all the unionized factories of G.M., Ford and Stellantis and of those companies’ 150,000 U.A.W. members.
This limited strike, however, could hamper the automakers because the sites produce some of their most profitable trucks, such as the Ford Bronco sport utility vehicle and Chevrolet Colorado pickup. And Mr. Fain has made it clear that the walkout could grow wider as contract accords remain elusive.
“This is certainly a different approach, and Fain is talking tough and has got tough proposals,” said Dennis Devaney, a former member of the National Labor Relations Board who is a labor lawyer at Clark Hill in Detroit.
The affected plants include a G.M. plant in Wentzville, Mo., that makes the GMC Canyon as well as the Colorado, and Stellantis’s complex in Toledo, Ohio, which makes the Jeep Gladiator and Wrangler. At Ford’s Michigan Assembly plant in Wayne, which makes the Bronco alongside the Ranger pickup, only workers from the assembly area and paint shop will walk out, Mr. Fain said.
The G.M. plant employs about 4,000 hourly workers, and the Stellantis plant about 4,400. Ford’s Michigan Assembly Plant employs about 2,800 hourly workers. It was unclear how many of that total work in the areas covered by the strike.
The union has demanded a 40 percent wage increase over the next four years, pointing out that the compensation packages for the chief executives of the three companies have increased about that much on average over the last four years.
Mr. Fain, who took office as union president this year, has also called for cost-of-living adjustments that nudge wages higher in response to inflation, shorter workweeks, improvements to retiree pensions and health care, and job security measures like the ability to strike at plants that are designated for closing. In addition, he wants changes to a wage scale that starts new hires at about $17 an hour and requires eight years for them to climb up to the top U.A.W. wage of $32 hour.
So far, the manufacturers have met Mr. Fain about halfway on wages but have opposed almost all of the other demands.
On Thursday, G.M. said its latest offer included a 20 percent wage increase over the life of the new contract, including a 10 percent raise in the first year, and cost-of-living adjustments, but only for more senior workers. G.M. also said it would allow new hires to reach the top wage after four years on the job.
“We put forward a compelling and unprecedented offer,” G.M.’s chief executive, Mary T. Barra, said in a video posted to a company website Thursday night. “It addresses what you’ve told us matters most: wage growth, job security and long-term stability.”
She also suggested that meeting most or all of the union’s demands could hurt the company’s prospects as it invested tens of billions of dollars in its transition to electric vehicles.
“We are at a crossroads on our path to transform the company,” she said. “Make no mistake: If we don’t continue to invest, we will lose ground, and it will happen fast. Nobody wins in a strike.”
Ford and Stellantis also made new proposals to the union in the 48 hours before the deadline but did not release details.
The Biden administration said Thursday that President Biden had spoken with Mr. Fain and with leaders of the auto companies about the status of the negotiations. A senior White House official said that Mr. Biden was not pressing the companies or the union on the particulars, but that he was encouraging all parties to stay at the table and to make sure that workers got a fair contract.
The union’s demands for significantly higher pay and new benefits are a sharp departure from the past 20 years, when the automakers were ailing and the U.A.W. was forced to accept major concessions to help the companies survive.
But more recently, G.M., Ford and Stellantis have been reporting near-record earnings. In the first half of this year, Ford made $3.7 billion and G.M. made $5 billion. Stellantis reported profits of 11 billion euros (about $11.9 billion).
Mr. Fain, who came up as an electrician at Chrysler and worked in the union administration before he was elected president, campaigned by promising to take a more aggressive and confrontational approach to this year’s contract negotiations.
In speeches to union members, he has frequently highlighted the pay of the automakers’ chief executives. Last year, Ms. Barra took home $29 million. Jim Farley of Ford made $21 million, while Stellantis’s chief, Carlos Tavares, was given a package worth about $25 million.
An extended strike would crimp the availability of new cars and drive up prices. A long stoppage would also ripple through the automakers’ supply chain and could hurt other businesses as workers live off $500 per week in strike pay from the union.
The auto industry is still dealing with the lingering effects of the pandemic. Production halted after the coronavirus hit, sharply reducing the supply of vehicles, and domestic car inventories are about a quarter of the stock at the end of 2019.
Michael D. Shear contributed reporting.