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The "Say Anything" actor delivered a grave warning to his 1.6 million Twitter followers on Tuesday about the alleged dangers of the 5G network and beliefs that it can negatively impact a person's immune system.
"5 -- G wil (sic) be proven to be very very bad for people's health," the award-winning actor wrote, according to the New York Post.
While the actor appears to have since scrubbed the tweet from his account, Cusack claimed that those close to him have knowledge that exposure to 5G networks can weaken the immune system, and in turn, make people more at risk of contracting COVID-19.
"I got sources in scientific community -- and medical," the actor further claimed on the platform before referring to his critics as "just DUMB and "f---ing Sheep."
The "High Fidelity" star did not make mention of the coronavirus pandemic in the since-deleted tweets, but his words come on the heels of numerous celebrities who have also shared their concerns with 5G in recent weeks as the pandemic escalates around the world.
Rapper M.I.A. appears to be one of the most vocal stars pushing the conspiracy theory on her own public platform.
"If you are in Islington/hackney please help call local authority to stop 5G work while we are in quarantined in our homes trying to be healthy. What we need now is Heath shelter nature food our community. This can not be corporate interests time again. Its about health of humans," the British singer wrote last month.
In response to fans' criticism of her views, M.I.A. said she doesn't believe 5G "gives you COVID19" but that it "can confuse or slow down the body during the healing process" amid the global pandemic.
"Cheers" star Woody Harrelson also touted concerns with 5G radiation, claiming on Instagram that it is "exacerbating" the virus' spread, according to the outlet.
The theory has been blamed for a series of arson attacks on phone towers in the United Kingdom, with Cabinet Minister Michael Gove dubbing the idea "dangerous nonsense," the Post said.
This isn't the first time Cusack's tweets have raised eyebrows. Last June, the actor faced backlash for a tweet critics called anti-Semitic. He later claimed a "bot" was to blame for the post.
Meanwhile, Cusack's political views are still clearly visible on his Twitter account, with the actor retweeting several tweets from others backing Bernie Sanders, who announced on Wednesday the suspension of his 2020 presidential campaign.