Hollywood's actors and writers have joined forces after studios failed to reach a deal with the Screen Actors Guild or Sag-Aftra, the American labour union headquartered in Los Angeles.
It is the first time that the two unions have been on strike simultaneously since 1960, when actor and future US president Ronald Reagan led the protests.
What does this double strike mean for Tinseltown?
Among Sag-Aftra's 160,000-strong ranks are many of the world's biggest stars.
Hollywood's A-list actors, from Tom Cruise to Angelina Jolie and Johnny Depp, are card-carrying union members.
Celebrities including Meryl Streep, Ben Stiller and Colin Farrell have come out publicly in favour of a strike.
On Thursday, Cillian Murphy, Emily Blunt and Matt Damon were among stars who staged a walkout from the UK premiere of Oppenheimer to join the strike. The film's other major stars, including Florence Pugh, Robert Downey Jr, Sir Kenneth Branagh and Rami Malek also left before the screening of the film at the Odeon Luxe in Leicester Square, London.
Ahead of the screening, Blunt warned that the cast would be leaving “in unity” if the strike was announced.
“I hope everyone makes a fair deal and we are here to just celebrate this movie,” she told Deadline in an interview. “We'll be leaving together as a cast in unity with everyone.”
But will we see them on the picket lines?
Top stars do not stand to gain financially from the strike, because their agents negotiate individual contracts with studios that far exceed the union minimums being fought over.
Still, their presence can "shine a light more on the studios, to come to the negotiating table with a fair deal," actor Dominic Burgess says.
"There will be visibility from the big stars," adds entertainment industry lawyer Jonathan Handel.
"But this strike is not about bringing more money to people who already have millions."
Why did the talks with actors' guild break down?
Hollywood actors were "duped" into extending negotiations for two weeks by studios who wanted more time to promote their summer blockbuster movies, union president Fran Drescher said on Thursday.
Sag-Aftra last month postponed their initial strike deadline, in the hope of thrashing out a deal with the likes of Netflix and Disney over demands for better pay and more protection against artificial intelligence.
That extension failed to yield any progress in talks, which collapsed on Wednesday night, with the union representing about 160,000 performers calling a strike for midnight Thursday.
"We, in good faith, gave them an extension, with the hope that they would make deep inroads, and we would really have something to discuss," said Drescher, the star and co-creator of 1990s sitcom The Nanny.
"But we were duped. They stayed behind closed doors, they kept cancelling our meetings, wasting time."
"It was probably all to have more time to promote their summer movies. Because nothing came out of it that was significant."
During that two-week period, major premieres have been held around the world for summer blockbuster films, including Warner's Barbie, Universal's Oppenheimer and Paramount's Mission: Impossible – Dead Reckoning Part One.
Sag-Aftra rules prevent actors from promoting their movies and shows during a strike.
Had the strike begun earlier, stars such as Cruise, Margot Robbie and Ryan Gosling would have had to skip glitzy red carpet events – a key tool used by studios to drum up publicity and, hopefully, box office receipts.
Red-carpet premieres set for the next few weeks are now being canceled, such as Paramount's Special Ops: Lioness, or scaled back, like Disney's Haunted Mansion.
What's at stake?
Hollywood productions have already slowed down significantly since the writers' strike began in early May.
Shows with finished scripts, such as The Lord of the Rings: The Rings of Power, were able to continue filming this summer, though without any writers on set.
But without actors, the only US-based productions that can continue are a handful of soap operas – which have a different contract – and reality and game shows.
For this reason, Fox this week unveiled an autumn television schedule full of unscripted series such as Kitchen Nightmares and Lego Masters.
From accounting to catering to transport, countless businesses are tied to the entertainment industry.
That makes the financial impact of a Hollywood strike hard to calculate, but incontrovertibly enormous.
"Fifteen years ago, when the writers were on strike – it was a 100-day strike – and the estimate was a little over $2 billion. So that translates to $20 million a day," says Handel.
Adjusted for inflation, that's close to $30 million a day lost in California alone, he adds.
"Believe me, our heart bleeds that we had to make this decision," said Drescher.
"But we can't not get what these members deserve, because it's only going to get worse.
"This is where we drew the line in the sand and it's a terrible thing to have to do. But we were forced into it."
Movie releases are less immediately affected, because of the long lag between the end of filming and the start of screening in theatres.
But the longer the strike goes on, the greater the impact on movie releases.
Major Hollywood studios have already reshuffled their release calendars. For instance, Disney recently pushed back several Marvel superhero films, spreading them out across a longer time period.
Sag-Aftra has suggested it could offer waivers to exempt smaller, truly independent films.
The strike also prevents members from promoting TV and motion pictures, meaning that premieres and important fall film festivals such as Venice and Toronto will be affected unless the strike ends.
So how long will this stoppage last?
Writers have already been manning the picket lines for 11 weeks.
But historically, Hollywood strikes have varied wildly in length – from several months to a little more than three hours.
"It's up to them if they're willing to talk in a normal way that honours what we do," Drescher said at a press conference on Thursday, referring to the studios. "We're open to talking to them tonight!"
Handel predicts the strikes will last at least until the autumn.
"This is going to drag on, and is not easily resolved, because both sides view this as existential," he says.
"There's a lot of bitterness between the writers and the studios, and the actors and the studios."
Agencies contributed to this report