Hollywood’s 15 years of labor peace was shattered Tuesday, as movie and television writers went on strike, bringing many productions to a halt and dealing a blow to an industry that has been rocked in recent years by the pandemic and sweeping technological shifts.

The unions representing the writers said in a statement, hours before their three-year contract expired at midnight Pacific time, that they had “voted unanimously to call a strike.” Writers will begin walking picket lines on Tuesday afternoon.

The Alliance of Motion Picture and Television Producers, which bargains on behalf of Hollywood companies, said in a statement that its offer included “generous increases in compensation for writers.” The organization added that it remained willing to keep negotiating.

The primary sticking points, according to the studios, involve union proposals that would require companies to staff television shows with a certain number of writers for a specified period of time “whether needed or not.”

The unions representing the writers, the East and West branches of the Writers Guild of America, said “the companies’ behavior has created a gig economy inside a union work force, and their immovable stance in this negotiation has betrayed a commitment to further devaluing the profession of writing.”

Chris Keyser, a co-chair of the W.G.A. negotiating committee, said in an interview that “philosophically, and practically, we’re very far apart.”

The dispute has pitted 11,500 screenwriters against the major studios, including old guard entertainment companies like Universal and Paramount as well as tech industry newcomers like Netflix, Amazon and Apple.

The W.G.A. painted the dispute in stark terms, saying that the ascendance of streaming services and the explosion of television production have eroded their working conditions. It has described this as an “existential” moment, and that “the survival of writing as a profession is at stake in this negotiation.”

Entertainment companies, which had previously said they were approaching the talks with “the long-term health and stability of the industry as our priority,” are confronting a rapidly changing business as network and cable television viewership plummets.

For viewers, the most immediate effect will be felt on talk and sketch shows. Late night shows like “Saturday Night Live,” “The Tonight Show Starring Jimmy Fallon” and “The Late Show With Stephen Colbert,” will likely go dark immediately. Reality series and some international shows, which are not covered by the guild, will be aired in heavy rotation.

It would take a long strike before there is a slowdown in the arrival of new TV shows and movies, because the production process for them can take months or more than a year.

A prolonged production shutdown could also prove damaging to local economies, particularly the workers who help support productions, such as drivers, costume dry cleaners, caterers, set carpenters and lumber yard workers. When the writers last went on strike, for 100 days in 2007, the Los Angeles economy lost an estimated $2.1 billion.

Seth Meyers, the host of NBC’s 12:30 a.m. late night show, alluded to the devastation of the last strike in a segment late last week.

“It doesn’t just affect the writers,” Mr. Meyers said in the web-only video. “It affects all the incredible nonwriting staff on these shows. And it would really be a miserable thing for people to have to go through, especially considering we’re on the heels of that awful pandemic.”

Mr. Meyers said he was a proud member of the W.G.A., and that he felt strongly that what the writers were asking for was “not unreasonable.”

“If you don’t see me here next week, know that it is something that is not done lightly, and that I will be heartbroken to miss you as well,” he said.

The writers have raised numerous grievances. In a very of-the-moment twist, the writers are seeking to put significant guardrails around the use of artificial intelligence. But the most pressing issue to them is compensation.

Over the last decade, a period that is often referred to as Peak TV, the number of scripted television shows broadcast in the United States has risen sharply. Writers, however, said that their pay has stagnated.

In the network television era, a writer could get work on a show with more than 20 episodes a season, providing a steady living for an entire year. However, in the streaming era, episode orders have declined to 8 or 12, and the median weekly pay for a writer-producer has gone down slightly, the W.G.A. said.

The writers want to also fix the formula for residual payments, which have been upended by streaming. Years ago, writers could receive residual payments whenever a show was licensed — into syndication or through DVD sales. But global streaming services like Netflix and Amazon have cut off those distribution arms, and pay a fixed residual instead.

The unions have taken particular aim at so-called minirooms, which have proliferated over the last decade. There is no one definition of a miniroom. But in one example, studios convene a small group of writers before a show has been given an official green light to compose a script. But writers are often paid less to work in minirooms, W.G.A. officials have said.

Writers have also said that the sudden growth of minirooms has also disrupted the decades-long art of learning how to make a television show. Mike Schur, the creator of “The Good Place” and co-creator of “Parks and Recreation,” said in an interview that when he was a young writer on “The Office,” he learned how to write a script, rewrite, edit, work with actors and became familiar with specialized crafts like set design and sound mixing.

“This is not stuff you can read in a book,” he said. “This is stuff that you have to experience.”

But because of minirooms, writers are sent home after as little as 10 weeks, and frequently are not around for the production process at all, he said.

“These companies don’t understand what is coming down the pike,” he said. “And what’s coming down the pike is an entire generation of show creators who might be super talented, who might have a lot to say about the world, but who functionally do not know how to do the job that they are going to be asked to do.”

Studio executives, however, have said privately that they have their own share of problems, and this is not the best time to be giving significant raises.

For several years, Wall Street rewarded media companies for investing in their streaming services at any cost in order to grow their subscriber pool. But investors soured on that philosophy last year, prompting studio executives to find a way to turn their money-losing streaming services into profit engines.

The fallout has been brutal. Disney is in the process of laying off 7,000 employees. Warner Bros. Discovery laid off thousands and shelved titles last year as it tries to pay down a debt load of around $50 billion. Other media companies have adopted similar cost-saving measures.

With that said, executives have also contended that they can weather a strike. Last month, David Zaslav, the chief executive of Warner Bros. Discovery, said, “We’ve got ourselves ready, we’ve had a lot of content that’s been produced.” Two weeks ago, Ted Sarandos, the co-chief executive of Netflix, suggested the streaming service would be better protected than his competitors because of how many unscripted and foreign series it has in production. “We could probably serve our members better than most,” he said.

Still, he conceded the consequences from a strike would be significant.

“The last time there was a strike, it was devastating to creators,” Mr. Sarandos said. “It was really hard in the industry. It was painful for local economies that support production and it was very, very, very bad for fans.”

Screenwriters have walked out six times over the decades. Historically, they have had the stomach for a prolonged strike. In addition to the 100-day walkout in 2007, the writers also walked picket lines for 153 days in 1988. Writers have also shown signs of remarkable unity. In mid-April, 98 percent of more than 9,000 union-represented writers authorized a strike.

The writers will hold demonstrations in New York and Los Angeles, where most entertainment companies are based.

Images of picket signs have already floated onto social media, with slogans like “Scripts Don’t Grow on Trees!” and “The Future of Writing Is at Stake!”