After four weeks of working as a background actor on the Disney+ series WandaVision during the pandemic, Alexandria Rubalcaba was told by the production crew to report to a tractor trailer.

Dozens of other background actors were wrangled to the same site, where, one by one, they were told to step in front of a series of cameras on metal rigs behind glass.

"Have your hands out. Have your hands in. Look this way. Look that way. Let us see your scared face. Let us see your surprised face," Rubalcaba, 47, recalls of the instructions she was given.

Rubalcaba said the actors had their faces and bodies scanned for about 15 minutes each. Then their digital replicas were created.

But here's the rub: She was never told how or if this digital avatar of herself would ever be used on screen. If it's used, she might never know. No matter what happens with it, she'll never see any payment for it.

Disney did not return a request for comment.

Rubalcaba, who makes the SAG-AFTRA union rate of $187 a day as a background actor, said she did not give permission for her digital replica to ever be used in the background of any scenes.

"What if I don't want to be on MarioVision, or SarahVision?" she said, rattling off made-up future productions. "I fear that AI is eventually going to weed out background actors. They won't have any use for us anymore."

The potential for artificial intelligence to replace background actors is one of the central tensions in the ongoing SAG-AFTRA strike with studios, the biggest labor dispute in Hollywood since the 1960s.

Background actors caught off guard by body scans

Background actors are not part of what's known as the "principal cast," meaning they do not have speaking parts and primarily serve to create realistic atmosphere by filling out a scene.

A union negotiator has claimed studios have offered to give background actors one day's pay after being scanned and that the actor's digital likeness could then be re-used "for the rest of eternity."

The studios have strongly taken issue with this characterization, claiming a background actor's digital replica would only be used on projects the performer was hired for, not indefinite future productions.

Either way, the practice of body-scanning background actors appears to be becoming more common. Five background actors interviewed by NPR all said they were caught off guard in recent months by having to undergo body scans by studios, feeling like they didn't have much of a choice, because if they pushed back, they feared the risk of retaliation. Most of the actors were were required to sign non-disclosure agreements.

"You don't know what's going to get back to casting. You don't know if they're going to call up casting and say, 'Oh this person is being difficult,' and not hire them again because that's how the system works," said Rebecca Safier, a background actor in Los Angeles who recently had her body scanned on set. "It's getting into this gray area of, 'what are they going to use it for in the future?'"

An 'existential threat' to background actors

Hollywood has long relied on high-tech tinkering to enhance films in post production. The producers of Games of Thrones and Lord of the Rings have fashioned large battle armies by relying on computer software that creates hordes of synthetic fighters.

And now that tech giants are in the movie-making business, they are doing it, too. For instance, Apple filled a stadium with what looked like 26,000 people by using digital doubles of just 20 background actors.

This method, known as "crowd tiling" is not new. For years, studios have used it shoot large group scenes.

But now with the technology taking strides forward with the advent of generative AI — which can create new conversations, images and videos by synthesizing an immense corpus of data with souped up hardware capable of harnessing an incredible amount of computing power — it is not only crowd scenes that are being digitally created.

There are AI-powered film editing tools that let film-makers move an actor's performance from one scene to another or replace dialogue. Other AI tools can make an actor's lips move as if they are speaking in an overdubbed language. Disney has an AI tool that can convincingly make an actor look younger or older in seconds.

One of most controversial uses of AI in Hollywood is digital cloning. Voices, faces and entire bodies can now be digitally re-created in ways that appear stunningly realistic.

Background actors in Hollywood say they worry they will be first in the industry made obsolete by AI.

Andrew Susskind, a associate professor at Drexel University's film and TV department who spent 30 years as a producer and director, said the widespread use of digital extras could impact budgets in significant ways.

"Imagine ballroom scenes, party scenes, any scenes that need tons of extras," Susskind said. "Imagine the amounts of money they would be saving. Not paying $180 a day. Plus meals. Plus costuming."

Because there presently are no rules of the road for how studios use AI, Susskind said it makes sense that actors, and writers have made AI a central sticking point in the Hollywood strikes.

"The actors, extras and the writers are right to see this moment as their best chance to set up what the rules should be in the use of AI," he said. "And the people in the background, who tend to have no real power and are treated badly, should be standing up for themselves here."

Katrina Sherwood, who works as a stand-in, body-double and background actress in Los Angeles, said she is distressed that AI will one day force her into another industry altogether.

"Our likeness is really the only thing that we actually own, so, for background, that would be an existential threat," she said.

About 84,200 of SAG-AFTRA's 160,000 active members have performed background work at some point in their career. Last year, more than 30,000 SAG members did at least one gig as a background actor.

Unions and studios disagree over AI consent

SAG-AFTRA is not resisting AI altogether.

Union officials have said that a digital replica of an actor could allow for an actor to be at two shoots at once, or take on a project they would not have done otherwise. But union officials say they will only support a contract that ensures adequate compensation to actors for their likeness being used.

The Alliance of Motion Picture and Television Producers, the trade group representing studios and producers, said they will offer "fair compensation" if an actor's digital replica is used. They say they will only use such AI creations after receiving permission from the actor.

Yet both sides are at odds over the meaning of consent. Studios are proposing that they will ask for background actors' permission once — after they are hired. Union officials say any use of an actor's digital replica should be bargained separately each time the digital likeness is used.

Dom Lubsey, a Los Angeles actor who does primarily background work, said unlike principal actors, extras do not have much say over how their performances are reused.

"I don't often hear people speaking up for background [actors], or if they're being abused, if they're not being treated properly, of if they should be paid more," he said. "You just don't hear that."

He said it is something that goes through his head every time his face and body has been scanned on set. The first time it happened was on the set of a popular racing moving, in 2019. Mostly recently, he was scanned for a television program about basketball.

"They wanted me to do cheering. I had to make angry faces. They asked for a war-cry faces. I did it all," he said.

After that, he felt a little rattled. He stepped out of the semi-truck trailer where a large cylinder outfitted with hundreds of small cameras had just scanned his various gestures as a game audience member. Perhaps the cost of doing business in Hollywood in the AI era, although is it also a step closer to his professional extinction, he wondered?

"My first thought leaving the trailer was, 'Oh this might just be the future," Lubsey said. "We might just lose our jobs."