G.M. also has to control costs because it is spending heavily to develop electric and self-driving cars. In the conference call, Ms. Barra said the automaker was likely to spend more on electric vehicles over the next five years than on gasoline-powered vehicles. The company’s autonomous-vehicle division, Cruise, lost $300 million in the third quarter.

[G.M. on Monday sided with the Trump administration in its clash with California over pollution standards.]

In exchange for an agreement to close plants, the new labor contract gives G.M.’s 49,000 U.A.W. workers pay increases over the next four years, including substantial jumps for about a third of its hourly workers who currently earn considerably less than the top wage of $31. After four years, most hourly workers will earn the new top wage of $32.

Analysts estimate that the contract will increase G.M.’s labor costs by about $100 million a year. Ms. Barra said G.M. aimed to cut costs to increase productivity to ease the impact of the higher labor costs. “I have asked the G.M. team to find every offset,” she said.

G.M. shares gained more than 4 percent in Tuesday’s trading.

The U.A.W. now has to reach deals with Ford Motor and Fiat Chrysler, and it will seek to win similar terms, an approach known as pattern bargaining. It is unclear whether those automakers will agree to the same terms or what they would seek in return, since neither has domestic plants designated for closure.

G.M. reported third-quarter net income of $2.3 billion, down 9 percent from $2.5 billion in the same period in 2018. The decline reflected the impact of the strike, which halted production in the final two weeks of the quarter, as well as a loss by overseas operations and higher warranty costs.

On an adjusted basis, the company earned $1.72 per share in the quarter, which ended Sept. 30, compared with $1.87 per share in the same quarter last year. Revenue declined to $35.5 billion from $35.8 billion.