The United Automobile Workers union announced Wednesday that it had reached a tentative agreement with General Motors on a new labor contract that could end a monthlong strike that has idled G.M. plants across the Midwest and South.
Details of the contract terms were not released, although the union said it had “achieved major wins.” There was no immediate announcement from G.M.
The move does not bring an immediate end to the strike. Contract terms still needs to be approved by the union leadership, then ratified by a majority of the 49,000 U.A.W. members employed by G.M. The union had summoned officials of G.M. locals to a meeting on Thursday in Detroit.
“Out of respect for our members, we will refrain from commenting on the details until the U.A.W. G.M. leaders gather together and receive all details,” Terry Dittes, the union’s chief G.M. negotiator, said in a statement.
The walkout, the first against a Detroit automaker’s nationwide operations since 2007, has left a mounting economic toll since it began on Sept. 16. It has cost the union, its members and G.M. itself hundreds of millions of dollars in lost dues, wages and revenue, as well as idling truckers and suppliers that serve the automaker.
The tentative agreement, if it becomes final, would solve the most immediate challenge facing G.M.’s chief executive, Mary T. Barra, and should provide certainty in calculating labor costs over the next four years. But she must contend with issues on other fronts, including a sales slowdown in the United States and China, and the need for big investments in electric vehicles and self-driving cars. And like other automakers, G.M. has continued to feel heat from President Trump over decisions on plant closings and foreign production.
The stakes were also high for the union. It faced discontent in its ranks over what members saw as a failure to win a fair share of the gains G.M. has made since its bankruptcy a decade ago.
If the General Motors contract is ratified, the U.A.W. will turn its focus to Ford Motor or Fiat Chrysler. Contracts with those manufacturers expired on Sept. 14, but workers have continued reporting to assembly lines while the union negotiated with G.M.
The U.A.W. is likely to try to hammer out similar terms with Ford and Fiat Chrysler, a standard practice known as pattern bargaining. The union chose G.M. as its target because the company has closed plants in the United States this year, and over the last several years has substantially increased production of vehicles at its four plants in Mexico.
Talks with Ford and Fiat Chrysler may be smoother because those companies have done less than G.M. to shift production south of the border. Ford, in fact, canceled plans to build a new plant in Mexico, and Fiat Chrysler has chosen to build a new Jeep factory in Detroit.
In the last five years, as American consumers flocked to high-margin trucks and sport utility vehicles, both G.M. and its unionized work force have prospered. In the last three years, G.M. has made $35 billion in profit in North America, and workers have been given annual profit-sharing checks averaging $11,000.
But even though G.M. was scaled down in bankruptcy, it still has excess production capacity. The company has enough plants to make about one million more vehicles than it is selling, according to the Center for Automotive Research, an independent, nonprofit group.
At the same time, G.M. is spending heavily to develop electric vehicles and self-driving technology, and its business outlook is uncertain. Auto sales have slowed in the United States, and some analysts expect a substantial decline in new-vehicle sales in 2020. Sales in China, the world’s largest auto market, have also softened.
Mark Wakefield, a managing director at AlixPartners, a consulting firm with a large automotive practice. said automakers were expected to spend some $225 billion over the next five years on development of electric and self-driving vehicles. “Industry profit is still good, but it’s down from its peak of a few years ago,” he said. The combination of heavy spending and slowing sales “has created some problems for them.”
That’s one reason that G.M. has been eager to retain flexibility in the size and deployment of its work force. Among the issues in dispute was the extent of G.M.’s use of temporary workers — now 7 percent of its head count — and their path to full-time status.
Marisol Gonzalez-Bowers worked for G.M. at Lordstown, Ohio, for about 24 years, most recently in “materials,” transporting parts to the assembly line. Relocating after the shutdown, she recently took a job at the company’s Lansing Delta Township plant in Michigan, where she was trained to assemble the insides of doors — the wires and plugs. Her trainers were almost all classified as temporary workers, she said, though they had been there four years.
“They’re working their butts off,” Ms. Gonzalez-Bowers said — and “making half my wages.”
Most temporary workers earn $15 an hour, compared with roughly $31 an hour for workers hired before 2007. Most permanent workers hired after 2007, known as “in progression” workers, earn about $17 to $25 an hour.
Veteran workers are guaranteed pensions in retirement. In-progression and temporary workers have 401(k) accounts to which they contribute.
Robin Sweet, an employee at a Ford Ranger plant in Wayne, Mich., said workers were upset at both the automakers and the union for not doing more to make them whole after the concessions made during the last downturn. “We want that money back in our pay,” Ms. Sweet said in a text message.
The agreement with G.M., even if followed by accords with Ford and Fiat Chrysler, won’t end the strain on the U.A.W. president, Gary Jones, and several of his top lieutenants. A federal criminal investigation has yielded corruption charges against several union officials over the last four years, including a union vice president who was sentenced to 15 months in prison.
The scandal “is concerning to the membership,” said Kristin Dziczek, vice president for industry, labor and economics at the Center for Automotive Research. “It’s cast a shadow, and hangs over the union, and appears to ensnare high-ranking officials.”
The G.M. strike was the latest push by labor for a larger share of the billions of dollars in wealth created as the United States recovered from the recession of a decade ago.
On Saturday, about 3,600 U.A.W. members went on strike at Mack Truck plants in three states, demanding better wages and benefits.
Last year, teachers in West Virginia, Oklahoma, and North Carolina secured better working conditions after walking off the job. And grocery workers in Southern California narrowly averted a strike this month when the United Food and Commercial Workers union reached a deal with several California supermarkets. The new contract includes wage increases totaling $1.55 to $1.65 an hour over three years, as well as improved health care benefits and pension contributions.