The International Alliance of Theatrical Stage Employees’ crew members working in the U.K. are preparing to down tools if the strike goes ahead on Oct. 18, Variety has learned.

Bectu, which represents the U.K.’s below-the-line workers, has confirmed it has received calls from heads of department (HODs) on U.K. productions asking about replacing IATSE workers in the U.K. The British union will advise members not to replace any striking IA members, said Spencer MacDonald, national secretary for the London production and regional production division of Bectu.

“Some HODs have been contacted about replacing IA members in the U.K.,” said MacDonald. “It appears they can strike, so we will be sending out a note to all our members about not replacing striking IA members.”

“Our members are fully behind IATSE,” said MacDonald. However, he said it was unlikely Bectu would strike in solidarity as that would require both a trade dispute and a balloting of Bectu’s members, which hasn’t happened.

Affected productions will be those covered by either the Producer-IATSE Basic Agreement or IATSE’s Theatrical and Television Motion Picture Area Standards Agreement, whose crew are members of IATSE.

Among the signatories to either or both of those agreements are Warner Bros. Pictures, which is currently filming “Aquaman 2” and “Wonka” in the U.K.; Legendary Pictures, which is shooting “Enola Holmes 2”; and Millennium Media, which is filming “The Expendables.”

Variety has reached out to Warner Bros. Pictures and Legendary for comment.

“Given the unprecedented nature of a potential nationwide film and TV worker strike, the full impact is difficult even for us to anticipate,” Jonas N. Loeb, communications director of IATSE’s New York branch told Variety. “We’re hoping the producers and studios continue working with us to make a deal that addresses core issues like reasonable rest periods, long hours, meal breaks and living wages so we are never forced to find out.”

IATSE is currently negotiating with the Alliance of Motion Picture and Television Producers ahead of a strike date on Oct. 18.

If negotiations falter, 60,000 union members will begin a nationwide — and potentially international — strike against the major studios that could bring the film and entertainment industry to its knees.

IATSE is asking for better hours and working conditions, including a turnaround time (the time between leaving set at night and returning the next morning) of 10 hours in order to prevent physical and mental harm resulting from exhaustion. Crew members have reported falling asleep at the wheel and even crashing their cars after spending long days and nights on set.

Meanwhile, Deadline reported that Bectu has formally asked its members to show solidarity with IATSE via an email sent by head Philippa Childs to members. In the mail, seen by Variety, Childs writes that the IATSE industrial action may involve IATSE members who are working in the U.K.

“If this does happen productions may try and replace them to cover their work. Bectu is fully behind IATSE and therefore we strongly recommend you contact the union if you are offered work of a striking IATSE member,” Childs writes.

“It is important that Bectu members do nothing to undermine the IATSE action and in fact we would ask you to go further and show your solidarity by taking a photo of yourself (with colleagues) and posting it on Facebook, Twitter and Instagram tagging @bectu @IATSE and with the hashtag #IASolidarity #UnionStrong,” Childs adds.

Bectu is currently negotiating its own trade agreements in the U.K., citing many similar issues.

Manori Ravindran contributed to this story.