A handful of Twitter users, backed by the Knight First Amendment Institute at Columbia University, sued President Donald Trump on Tuesday, claiming their constitutional rights are being violated because the president has blocked them from his @realDonaldTrump handle.

The suit claims that Trump's Twitter feed is a public forum and an official voice of the president. Excluding people from reading or replying to his tweets—especially because they tweeted critical comments—amounts to a First Amendment breach, according to the lawsuit.

"The @realDonaldTrump account is a kind of digital town hall in which the president and his aides use the tweet function to communicate news and information to the public, and members of the public use the reply function to respond to the president and his aides and exchange views with one another," according to the lawsuit (PDF) filed in New York federal court.

The suit, which adopts a unique constitutional theory about social media rights, comes a month after the Knight First Amendment Institute threatened to sue Trump unless the president unblocked its clients from what it called a "designated public forum." Being blocked from Trump's Twitter feed, they said, was illegal and akin to a mayor ejecting critics from city hall meetings.

Trump takes to Twitter to announce and denounce everything from North Korea missile launches to the latest domestic and foreign policy issues. The president announced the nomination of Christopher Wray to become FBI director on Twitter, and he even told his Twitter followers that he did not tape meetings with then-FBI Director James Comey. And just this weekend, the president sparked controversy when he tweeted that he wanted the US and Russia to create a joint "cyber security unit."

To date, Trump has amassed 33.7 million Twitter followers, up roughly two million from a month ago.

The new lawsuit also names White House Press Secretary Sean Spicer and Daniel Scavino, the White House director of social media.

"Defendants' viewpoint-based blocking of the Individual Plaintiffs from the @realDonaldTrump account infringes the Individual Plaintiffs' First Amendment rights. It imposes an unconstitutional restriction on their participation in a designated public forum," the suit says. "It imposes an unconstitutional restriction on their right to access statements that Defendants are otherwise making available to the public at large. It also imposes an unconstitutional restriction on their right to petition the government for redress of grievances."

The Knight First Amendment Institute is also a named plaintiff. Although it has not been blocked by Trump, the organization claims that it has a constitutional right to read the views of those who have been blocked.

"Defendants' viewpoint-based blocking of the Individual Plaintiffs violates the Knight Institute’s First Amendment rights by distorting the expressive forum in which the Knight Institute and other non-blocked users participate," the suit alleges.

The suit asks that a federal judge declare it unconstitutional to block people on Trump's feed. The lawsuit also demands that Trump be barred from blocking people on his Twitter feed.