A battle between Detroit carmakers and the United Auto Workers union, which escalated on Friday with targeted strikes in three locations, is unfolding amid a once-in-a-century technological upheaval that poses huge risks for both the companies and the union.

The strike has come as the traditional automakers invest billions to develop electric vehicles while still making most of their money from gasoline-driven cars. The negotiations will determine the balance of power between workers and management, possibly for years to come. That makes the strike as much a struggle for the industry’s future as it is about wages, benefits and working conditions.

The established carmakers — General Motors, Ford Motor and Stellantis, which owns Chrysler, Jeep and Ram — are trying to defend their profits and their place in the market in the face of stiff competition from Tesla and foreign automakers. Some executives and analysts have characterized what is happening in the industry as the biggest technological transformation since Henry Ford’s moving assembly line started up at the beginning of the 20th century.

Nearly 13,000 U.A.W. workers walked off the job at three plants in Ohio, Michigan and Missouri on Friday after talks between the unions and the companies in three separate negotiations failed to result in agreements before a Thursday deadline. Pay is one of the biggest sticking points: The union is demanding a 40 percent pay increase over four years but the automakers have offered roughly half as much.

But the talks are about more than pay. Workers are trying to defend jobs as manufacturing shifts from internal combustion engines to batteries. Because they have fewer parts, electric cars can be made with fewer workers than gasoline vehicles. A favorable outcome for the U.A.W. would also give the union a strong calling card if, as some expect, it then tries to organize employees at Tesla and other nonunion carmakers like Hyundai, which is planning to manufacture electric vehicles at a massive new factory in Georgia.

“The transition to E.V.s is dominating every bit of this discussion,” said John Casesa, senior managing director at the investment firm Guggenheim Partners who previously headed strategy at Ford Motor.

“It’s unspoken,” Mr. Casesa added. “But really, it’s all about positioning the union to have a central role in the new electric industry.”

Under pressure from government officials and changing consumer demand, Ford, G.M. and Stellantis are investing billions to retool their sprawling operations to build electric vehicles, which are critical to addressing climate change. But they are making little if any profit on those vehicles while Tesla, which dominates electric car sales, is profitable and growing fast.

Ford said in July that its electric vehicle business would lose $4.5 billion this year. If the union got all the increases in pay, pensions and other benefits it is seeking, the company said, its workers’ total compensation would be twice as much as Tesla’s employees.

Union demands would force Ford to scrap its investments in electric vehicles, Jim Farley, the company’s chief executive, said in an interview on Friday. “We want to actually have a conversation about a sustainable future,” he said, “not one that forces us to choose between going out of business and rewarding our workers.”

For workers, the biggest concern is that electric vehicles have far fewer parts than gasoline models and will render many jobs obsolete. Plants that make mufflers, catalytic converters, fuel injectors and other components that electric cars don’t need will have to be overhauled or shut down.

Many new battery and electric vehicle factories are springing up and could employ workers from the plants that have shut down. But automakers are building most aggressively in the South where labor laws are tilted against union organizers, rather than in the Midwest, where the U.A.W. has more clout. One of the union’s demands is that workers in the new factories be covered by the automakers’ national labor contracts — a demand that the automakers have said they can’t meet because those plants are owned by joint ventures. The union also wants to regain the right to strike to block plant shutdowns.

“We are at the dawn of another industrial revolution and the way we’re going is the way we went in the last industrial revolution — a lot of profit for a few and misery and not good jobs for the many,” said Madeline Janis, executive director of Jobs to Move America, an advocacy group that works closely with the U.A.W. and other unions.

“The U.A.W. is really taking a stand for communities across the country to make sure this transition benefits everybody,” Ms. Janis added.

Automakers have been racking up record profits during the last decade, but they cannot afford to lose time from work stoppages in their race to compete with Tesla and foreign automakers.

The three companies are already struggling to get their electric vehicle business going. A new G.M. battery factory in Ohio has been slow to produce batteries, delaying electric versions of the Chevrolet Silverado pickup and other vehicles. Ford this year had to suspend production of its electric F-150 Lightning in February after a battery caught fire in one of the pickups that was parked near the factory for a quality check. And Stellantis won’t even begin selling any fully electric vehicles in the United States until next year.

Those problems and Tesla’s growing sales could put the union in a strong position to extract a good deal.

On Thursday, in a sign that automakers are willing to go much further than they had previously, G.M. offered a 20 percent pay raise over four years. That is half of what the union is seeking but far more than workers received in recent contracts. President Biden on Friday strongly supported the union in remarks at the White House. The administration has been pouring billions into programs to promote electric vehicles and does not want a strike to delay a centerpiece of its climate policy.

Despite all the money that automakers have made in recent years, their executives express a profound unease about the growth of electric vehicles, which account for 7 percent of the U.S. new car market so far this year and are on track to surpass sales of one million this year. Managers are acutely aware that traditional companies like theirs have a poor track record of retaining dominance after a big change in technology. Witness the way that Apple sidelined Nokia and Motorola as cellphones became smartphones.

Auto company executives and most industry analysts underestimated how quickly electric vehicles would catch on and cannot confidently forecast how sales, which have been bumpy lately, will grow in the future. “I don’t think anyone can perfectly predict what the adoption will be,” Mary T. Barra, the chief executive of General Motors, said in an interview with The New York Times last month.

Speaking to “CBS Mornings” on Friday, Ms. Barra said an excessive pay raise would undermine G.M.’s ability to continue producing vehicles with internal combustion engines while also developing electric vehicles. “This is a critical juncture where investing is very important,” she said.

Still, unions and their supporters are unlikely to express much sympathy for auto executives. Ms. Barra, Mr. Farley of Ford and the chief executive of Stellantis, Carlos Tavares, have gotten tens of millions of dollars in compensation packages in recent years. The companies’ shareholders have been rewarded with dividends and share buybacks.

Unions “are not going to have a lot of patience for sob stories,” said Karl Brauer, executive analyst at iSeeCars.com, an online marketplace.

Adjusted for inflation, wages for autoworkers in the United States have fallen 19 percent since 2008, according to the Economic Policy Institute, a left-leaning research group.

At the same time, union officials are aware of the changes in the industry and have said they do not want to handicap G.M., Ford and Stellantis as the companies try to recover ground they have lost to Tesla, which has aggressively resisted attempts to unionize its factories. The Detroit carmakers also face challengers like Rivian, a start-up that makes electric pickup trucks and sport utility vehicles in Illinois, as well as foreign-owned rivals like Mercedes-Benz and Toyota, whose U.S. factories, mostly in the South, are not unionized.

“That’s the biggest challenge here,” Mr. Brauer added, “trying to commit to a long-term contract in an industry that is very uncertain and unpredictable over the next five years.”

Union supporters say it would be wrong to blame workers if the traditional carmakers cannot compete with Tesla and other rivals.

“If you look at the breakdown at what it costs to build an E.V., labor is a very small part of the equation. Batteries are the most,” Ms. Janis of Jobs to Move America said. “This idea that the U.A.W. is going to price Ford, G.M. and Stellantis out of the market is not true.”

But other analysts said that a long work stoppage could help Tesla and foreign automakers gain ground on G.M., Ford and Stellantis.

“If something happens to disrupt their business, does that give a leg up to the emerging electric vehicle makers?” said Steve Patton, who overseas the consulting firm EY’s work with auto companies. “Who stands to benefit if there is a protracted strike?”