As COVID-19 cases rise in California, Sean Penn is issuing an ultimatum for Gaslit, the series he's starring in with Julia Roberts. The actor won't return to work on the Watergate drama until everyone on the production has been vaccinated for the virus, EW has confirmed.

Deadline first reported the news on Thursday, adding that Penn's organization CORE has offered to facilitate the vaccination effort for free. NBCUniversal, the studio behind the Starz limited series, mandated this week that vaccinations are mandatory in "Zone A," which constitutes the cast and those who come in close proximity. Gaslit is being shot mostly indoors in Burbank, Calif.

EW confirmed that Penn deemed this rule inadequate. The performer's absence means production will be delayed, as he has a few weeks left before wrapping.

Gaslit is an upcoming series inspired by Slate's podcast Slow Burn. It features Penn as Attorney General John Mitchell under President Richard Nixon, with Roberts playing John's wife Martha.

The series is created by Robbie Pickering and Mr. Robot's Sam Esmail, and sources told Deadline that the production has been sympathetic to Penn's request. The studio has adhered to safety protocols on set, but the sources also told the outlet that NBCUniversal might not have the legal latitude to impose mandatory vaccinations until the concern has been negotiated with Hollywood unions and other studios.

Representatives for Penn declined to comment further. NBCUniversal's UCP, the production company behind Gaslit, did not immediately respond to EW's request for comment.

Through CORE, Penn has been dedicated to coronavirus relief efforts during the pandemic, including putting together the largest testing system in Los Angeles. Recently, at a press conference for his film Flag Day at Cannes Film Festival, Penn lambasted Donald Trump's administration's response to the COVID-19 crisis.

"It really felt like someone with a machine gun gunning down communities that were the most vulnerable from a turret at the White House," Penn said.

"We were not only as a country but as a world, let down and ultimately neglected misinformed, had truth and reason assaulted under what was in all terms an obscene administration, humanly and politically," he added.

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