All this might help explain why a recent Gallup poll found that public approval for unions has climbed to 64 percent, up from 48 percent a decade ago and near its highest level in 50 years. An M.I.T. study last year found that nearly 50 percent of nonunion workers say they would vote to join a union if they could, up from 32 percent in 1995.

From the moment the G.M. walkout started, union leaders said the strike was bigger than just G.M. “Today, we stand strong and say with one voice, we are standing up for our members and for the fundamental rights of working-class people in this nation,” Terry Dittes, a United Automobile Workers vice president, said. The autoworkers are taking a page from the teachers, who made it clear that they were striking not just because they were tired of pay freezes but also to help their students, by increasing education budgets, reducing class sizes and replacing obsolete textbooks.

With many Americans angry about factories moving overseas, the autoworkers union also wants G.M. to reopen its giant plant in Lordstown, Ohio. The company closed the plant because demand for Chevy Cruzes had declined, even as it has kept open its plant in Mexico that makes the same car. And with many workers upset about the increased instability and precariousness of their jobs, the union is also pressing G.M. to stop using so many temps — they represent 7 percent of the company’s work force and make just $15 an hour.

Donald Trump won the 2016 election partly because many workers thought the system was rigged against them. That sentiment is also fueling the G.M. strike. The company had $8.1 billion in profits worldwide last year and $35 billion in North America over the last three years, so workers are resentful that the company nonetheless wants to close plants — especially when union members made major concessions, like creating a two-tier wage structure at some plants, to help lift the company out of bankruptcy.

But General Motors insists that it has already made a generous offer, saying it offered to add 5,400 jobs and make more than $7 billion in new investments in plants in the United States. “We have negotiated in good faith and with a sense of urgency,” G.M. said. “Our goal remains to build a strong future for our employees and our business.”