The last time Hollywood actors and screenwriters went on strike at the same time, Marilyn Monroe and Elizabeth Taylor were among its biggest stars.

Their films were temporarily halted, while the actors' union – led by Ronald Reagan, two decades before he became the US president – hammered out an agreement with studios.

Back then, performers were fighting for what are known as "residuals" — payments made to actors when their films were later broadcast on television.

Residuals became commonplace over the more than 60 years that followed, but streaming services have now up-ended the way they're paid.

Actors and writers are also grappling with a very modern challenge, warning they face an "existential threat" from artificial intelligence (AI).

Studios argue they have offered historic pay increases and "groundbreaking" AI protections, and that the strike will hurt thousands of other people who depend on the industry. 

But after weeks of failed negotiations, performers rejected their latest proposal and decided to walk off the job.

Why are actors going on strike?

Actors are represented by the union SAG-AFTRA, which is now led Fran Drescher, the star of 90s sitcom The Nanny.

"The entire business model has been changed by streaming, digital, AI," she told a press conference in Los Angeles.

"This is a moment of history, it is a moment of truth.

"If we don't stand tall right now, we are all going to be in trouble."

The union is demanding increases to base pay and residuals, arguing compensation over the past decade had been "severely eroded by the rise of the streaming ecosystem".

Kylie Sparks, who has spent 20 years in the industry after starting as a child actor, described residuals as being similar to royalty payments.

"Basically every time something re-airs, it triggers a residual cheque, or a movie does well and it triggers," they told the ABC.

"Same thing for DVD, so you'll get a percentage of your pay from DVD or digital buying, like if you buy from iTunes."

Actors argue streaming services pay much lower residuals than TV networks, while Sparks said they would not receive any at all from their work in the recent Netflix comedy I Think You Should Leave.

"Meanwhile, the other day I got a cheque for about $500 from an arc I did on Desperate Housewives in 2008," they said.

"So the fact that I am still making money from a show I did in 2008, but yet I won't see a dime from a show that has been watched millions of hours that came out in May, is unacceptable."

The rise of generative AI is another major concern, with actors worried about how their voice and likeness could be used without payment, or their consent.

Some fear AI will replace both background extras and post-production jobs, such as re-recording dialogue, that actors would normally be paid for.

LA-based Australian actor Zac Garred believed writers were in a "more precarious" position amid fears scriptwriting could be outsourced to AI tools.

But he said there were still a lot of unknowns for performers, too.

"We know that AI can write songs as Beyonce, we know that we can create a young Harrison Ford," he said, referring to the star's latest Indiana Jones film.

"Now that was with the consent [of Harrison Ford].

"The issue is the vast majority of working actors that make up around about 98 per cent of the union, and where our likenesses would be utilised with or without our consent."

What does the strike mean for your favourite movies and TV shows?

The 11,500 members of the Writers Guild of America have been on strike since May over similar concerns raised by actors.

The writers' strike has already led to major disruptions, with late-night shows like Saturday Night Live forced into running repeats and production paused on upcoming seasons of Abbott Elementary and Stranger Things.

Others, such as showrunner Ryan Murphy's series American Horror Story, kept filming, leading to protests outside.

But with actors now joining writers on the picket lines, most of the industry is expected to grind to a halt.

While some production work will continue, filming will cease and stars will stop promoting their TV shows and movies.

Pop culture event Comic-Con is expected to be scaled back, and actors are unlikely to attend film festivals.

Overseas TV and film productions could also be affected.

The writers' strike was recently cited as a reason for shutting down one of the largest productions ever planned for Australia, a TV series named Metropolis to be shot in Melbourne. 

The Media, Entertainment and Arts Alliance (MEAA) in Australia said it fully supported the action being taken in the US. 

"A small number of productions currently underway in Australia may be impacted by the SAG-AFTRA and Writers Guild of America strikes," MEAA chief executive Erin Madeleines said in a statement. 

"MEAA representatives are in dialogue with the producers of those productions and will advise crew and performer members of their rights if work is interrupted by the strikes."