The Screen Actors Guild (SAG-AFTRA), which represents 160,000 performers including A-list stars, said negotiations late Wednesday had ended without a deal on their demands over dwindling pay and the threat posed by artificial intelligence.
Its negotiators have unanimously recommended a strike to its national committee, who are expected to vote on Thursday morning.
The vote opens the door to a "double strike" with writers, who have already spent 11 weeks on the picket line -- which would trigger the first Hollywood shutdown since 1960.
Popular series set to return to television this year would face lengthy delays. And, if strikes continue, future blockbuster films would be postponed too.
Actors, like writers, are demanding better pay, and protections against the future use of AI in television and films.
"As you know, over the past decade, your compensation has been severely eroded by the rise of the streaming ecosystem. Furthermore, artificial intelligence poses an existential threat to creative professions," a SAG-AFRTA statement said after the talks fell through.
Industry executives have "refused to acknowledge that enormous shifts in the industry and economy have had a detrimental impact on those who perform labor for the studios," it continued.
"We are deeply disappointed that SAG-AFTRA has decided to walk away from negotiations. This is the Union's choice, not ours," the Alliance of Motion Picture and Television Producers said early Thursday.
Hollywood studios had called in federal mediators to help resolve the deadlock -- a move described by SAG-AFTRA as a "cynical ploy."
SAG-AFTRA represents A-list stars such as Meryl Streep, Jennifer Lawrence and Glenn Close. All members have pre-approved industrial action if a deal was not struck. The last time the union went on strike, in 1980, it lasted more than three months.
- Premieres and parties -
A strike would immediately prevent stars from promoting some of the year's biggest releases, right at the peak of the movie industry's summer blockbuster season.
In London, a premiere Wednesday night for Christopher Nolan's "Oppenheimer" was brought forward by an hour, so that cast including Robert Downey Jr., Matt Damon and Emily Blunt could attend without breaking union rules, Variety reported.
But a strike would derail the much-hyped film's US premiere, due to take place in New York on Monday, as well as a red-carpet launch this weekend at Disneyland for the new "Haunted Mansion" movie.
And the annual Comic-Con pop culture gathering in San Diego next week could be stripped of its stars.
Even the Emmy Awards, television's version of the Oscars, which is due to take place on September 18, is reportedly mulling a delay to November or even next year.
- 'Swift resolution -
While the writers' strike has already dramatically reduced the number of movies and shows in production, an actors' walkout would shutter almost everything.
Some reality TV, animation and talk shows could continue.
On Wednesday, Hollywood unions representing directors, behind-the-scenes film workers and writers issued a statement of "unwavering support and solidarity" with the actors.
"While the studios have collective worth of trillions of dollars, billions of viewers globally, and sky-high profits, this fight is not about actors against the studios," it said.
Workers "across all crafts and departments" stand together "to prevent mega-corporations from eroding the conditions we fought decades to achieve."
Actors and writers are demanding higher pay to counteract inflation, and guarantees for their future livelihoods.
In addition to salaries when they are actively working, actors earn payments called "residuals" every time a film or show they starred in is aired on network or cable -- helpful when performers are between projects.
But today, streamers like Netflix and Disney+ do not disclose viewing figures for their shows, and offer the same flat rate for everything on their platforms, regardless of its popularity.
Muddying the waters further is the issue of AI. Both actors and writers want guarantees to regulate its future use, but studios have so far refused to budge.