After negotiations between studio representatives the Alliance of Motion Picture and Television Producers (AMPTP) and the US actors’ union Sag-Aftra (Screen Actors Guild–American Federation of Television and Radio Artists) failed to make a breakthrough, Hollywood actors are going on strike.

The decision means that actors will be joining writers on the picket lines, marking the first time in over six decades that both unions have taken simultaneous strike action.

Considerable though the effect of the writers’ strike has been on film and TV production, as well as related activities such as awards shows and publicity events, an actors’ strike is likely to be seismic. Not least because Sag-Aftra’s reach is global: any film or show featuring a Hollywood actor is likely to have to shut down, or at least be massively rescheduled, when the strike begins at midnight on Thursday.

The writers’ strike has already seen the shutdown of the vast majority of scripted TV shows in the US, as picket lines have been largely successful at ensuring production activities have ceased. Series including The Last of Us, Blade Runner 2099 and The Mandalorian have already been delayed, while future projects – such as the sequel to Spider-Man: No Way Home, and Disney’s Blade remake – have also stalled, as scripts are not being completed. Others, including Thunderbolts and Captain America: Brave New World, are in production, but have had their release dates put back.

However, the withdrawal of US actors’ participation means that even productions with finished scripts can now no longer go ahead, whether in the US itself, Europe or elsewhere. According to Deadline, TV shows likely to be affected include House of the Dragon, Andor and Industry, while the second season of Sharon Horgan’s Bad Sisters will probably be unable to start shooting. Doctor Who, which is now being produced in partnership with the streaming service Disney+, is also likely to be affected by strike action.

Studio film productions, which run on even longer and more elaborate schedules, will suffer longer-term damage if they have not completed filming in time. The highest-profile films still shooting include the Ridley Scott-directed Gladiator 2, starring Paul Mescal, which was scheduled to shoot in Malta, Morocco and the UK between June and October, and Mission: Impossible – Dead Reckoning Part Two, the sequel to Tom Cruise’s hit blockbuster, which was due to finish shooting this summer after promotional duties on Part One were over.

Other studio productions, including the fourth Bad Boys film, Beetlejuice 2 and the untitled Ghostbusters: Afterlife sequel have reportedly finished shooting, as has the second season of Amazon’s TV series The Lord of the Rings: The Rings of Power.

The situation is more complex for low-budget and independent films, which may be able to apply for waivers from Sag-Aftra to allow them to go ahead. However, the uncertainty over who can work, and who can and can’t cross picket lines, has led to considerable financial instability in an already precarious sector. Even with a waiver, and an already completed script, productions cannot rely on the participation of crucial crew, as the transportation union the Teamsters, and technicians’ union Iatse, are mostly refusing to cross writers’ union picket lines.

Outside film-making activities, other high-profile events are likely to be altered or cancelled now that the actors’ union has called a strike. The London premiere of Christopher Nolan’s atom-bomb drama Oppenheimer has been moved forward by an hour tonight to ensure its cast can attend. And the popular Comic-Con event in San Diego – due to take place 20-23 July, and normally attended by large numbers of stars to promote their films to adoring fans – looks likely to be badly hit. Late summer releases such as Teenage Mutant Ninja Turtles: Mutant Mayhem, Haunted Mansion and Blue Beetle are also expected to have to curtail promotional activities. Major international film festivals – including Venice and Toronto, which take place nearly simultaneously in late August and early September – should be able to screen available films, but red carpet activity and actor appearances are now in doubt.

Televised awards shows are also facing problems. The writers’ strike already forced the postponement of the Daytime Emmy awards, due to take place in June, and although it is not scheduled to take place until 18 September, the Primetime Emmy awards, which are given to high-profile TV shows, look to be next in line, with the ceremony likely to be delayed at least until November. With the next Academy Awards not scheduled to take place until March 2024, the Oscars should remain unaffected unless the strike is a prolonged one.