Fetterman, a high-profile Democrat who is mulling a Senate run in 2022, slammed those who declared that his state was one of several that were "rigged" in favor of President-elect Joe Biden.
"This idea that saying that Pennsylvania was 'rigged' or that we were 'trying to steal the election,' that's a lie," Fetterman told The Hill. "And you do not have the right, that is not protected speech."
Fetterman argued that tweets by President Trump echoing the false claim should have been removed by Twitter "immediately" and insisted such an action was "not de-platforming" but rather "deleting lies that are yelling 'fire' in a crowded theater when there is none."
"That is not protected speech," Fetterman doubled down. "He can talk all day about what his favorite football team is or that he's the greatest president in the history of the world, but no one -- Republican, Democrat, or whatever -- has the right to say those kind of incendiary lies."
Critics were quick to fact-check Fetterman's remarks on social media.
"WARNING LABEL: 'This claim is determined to be ridiculously false.' Signed, US Constitution," journalist Sharyl Attkisson quipped.
"Getting really tired of being stuck between clowns insisting that certain bad/wrong speech being protected means we shouldn't condemn it and other clowns claiming that speech they don't like or that is bad should be illegal," conservative writer A.G. Hamilton reacted.
"Like it or not (guess which side I fall on), that IS protected speech. And it's irresponsible to aver otherwise," National Review podcast host Jeff Blehar tweeted.
"What if the lies about 'trying to steal the election' are published and echoed by the republic's most prominent media outlets, and are repeatedly debunked but nevertheless consistently revived by those outlets quoting anonymous officials, over half a decade? Hypothetically?" Ted Cruz national security adviser Omri Ceren asked, alluding to the media's years-long coverage of the Russian collusion narrative.
"This man is a statewide elected official? He shows zero grasp of the principles of free speech or the protections of the First Amendment," former Trump campaigna adviser Steve Cortes said.
Fetterman isn't the only prominent Democrat to suggest that spreading falsehoods about the 2020 presidential election should be illegal. Earlier this week, Rep. Alexandria Ocasio-Cortez, D-N.Y., floated a congressional "commission" to "rein in" the media's role in spreading what lawmakers would determine is "disinformation and misinformation."