The International Alliance of Theatrical Stage Employees is threatening to go on strike on Monday morning if it cannot reach a new contract. The strike will put up to 60,000 workers on the picket lines, shutting down film and TV production nationwide, and causing a lot of chaos.

It will be especially confusing in New York, where most workers from several IATSE-affiliated locals — including Local 52 and United Scenic Artists Local 829 — will not be on strike, even while other IATSE locals will be.

Local 52 represents about 4,500 workers, including electricians, grips and carpenters, in five states: New York, New Jersey, Connecticut, Delaware and Pennsylvania (except for Pittsburgh). USA 829 represents another 5,000 workers around the country, including costume designers and art directors who work in film and TV in the New York area. Both guilds work under their own contracts with the major studios, which are called Majors Agreements. Those contracts have not expired and will remain in force even if IATSE goes on strike on Monday.

But those members do work alongside camera operators, camera assistants, directors of photography and technicians from the International Cinematographers Guild, Local 600, which would be on strike. Those workers are expected to be picketing job sites on Monday morning, unless the Alliance of Motion Picture and Television Producers can strike a deal with IATSE by midnight on Sunday.

That means that non-striking IATSE members could be faced with a decision about whether to cross picket lines.

“How you respond to the picket line is your choice,” Local 52 told members in an email this week.

The Local 52 contract contains a provision — similar to the provision in Teamsters contracts — that grants members the right to refuse to cross picket lines.

“This provision was negotiated to provide each of you working under the Majors Agreement the right to make a personal choice as to whether to honor such a picket line,” the local told members.

It’s also not clear how employers will respond. If a show’s cinematographer goes on strike, the producers could simply shut down production — relieving the rest of the crew of having to make a choice. But they could also try to find a non-union cinematographer.

Meanwhile, shows like “Saturday Night Live” and other late-night shows are expected to continue production, because they are not covered by the expired contracts.

Jonas Loeb, a spokesman for the International union, said that the union itself was struggling to understand precisely how a strike would play out, and which shows would and would not be affected.

“The lack of precedent and complex patchwork of contracts within the industry makes it difficult to anticipate, even for us,” Loeb said. “The confusion around this speaks to how incredibly disruptive a strike has the potential to be, and we’re hoping to keep working with the studios to make a deal that addresses core issues like reasonable rest, meal breaks, living wages, and a fair share of streaming success so we are never forced to find out.”

Work is expected to continue on HBO shows, as well as shows made for Starz, BET and Showtime — as well as low-budget films and commercials.

Jazz Tangcay and Brian Steinberg contributed to this story.