Twitter users blocked by President Trump claim the president has no legal right to block them, citing the First Amendment.

The New York Times reports that users that have been blocked by President Trump on Twitter have taken legal issue with their ban, arguing that the Constitution bars the President from blocking people on the social media service.

They argue the fact that President Trump has used his @realdonaldtrump Twitter account to make statements relating to public policy, his account acts as a “public forum” which people may not be excluded from by the government simply because they disagree with the opinion expressed.

A letter was sent to President Trump on Tuesday by the Knight First Amendment Institute, who are representing the group of banned individuals. The letter states, “This Twitter account operates as a ‘designated public forum’ for First Amendment purposes, and accordingly the viewpoint-based blocking of our clients is unconstitutional.” It continues, “We ask that you unblock them and any others who have been blocked for similar reasons.”

The letter is not a formal declaration of legal action but does imply that if the users are not unblocked, legal action may follow. Jameel Jaffer, the Executive Director of the Knight First Amendment Institute at Columbia University, said in a statement, “Though the architects of the Constitution surely didn’t contemplate presidential Twitter accounts, they understood that the president must not be allowed to banish views from public discourse simply because he finds them objectionable.”

“Having opened this forum to all comers, the president can’t exclude people from it merely because he dislikes what they’re saying,” Jaffer said.

Holly O’Reilly, one of the main organizers of the anti-Trump protest March For Truth, was blocked by Trump following many critical comments on his statuses. In one tweet, President Trump discussed the British Prime Minister’s anger that information relating to the terrorist attacks in Manchester were leaked. “YOU ARE THE LEAKER, you bloody idiot. God, you’re embarrassing.” wrote O’Reilly.

YOU ARE THE LEAKER, you bloody idiot. God, you're embarrassing. So glad we are finally getting the TRUTH. https://t.co/RddfpVuPiU @marchfeed — Holly Figueroa O'Reilly (@AynRandPaulRyan) May 28, 2017

O’Reilly is one of many verified Twitter users that comment on Trump’s tweets, often criticizing the president or pushing unsubstantiated conspiracy theories. In another of President Trump’s tweets criticizing the mainstream media, United Press International writer Ben Hooper continued to push the conspiracy theory that Russia somehow spread “fake news” in order to benefit Trump.

https://twitter.com/BenHooperWrites/status/872065508572626945

If President Trump’s blocking of certain individuals leads to a legal challenge, Twitter could find themselves in an awkward position as a social media platform which has actively worked to provide their users with content moderation tools for individuals using the service. Twitter allows users to block others, censor “sensitive content,” and even mute certain keywords that they would rather not have appear on their timeline.

Twitter has had little issue with censoring conservative voices on its platform, however, as Breitbart Tech has reported:

Twitter’s bias against conservatives is well-known. The company frequently bans or locks the accounts of conservative users who have not broken its terms of service, while allowing threats of violence against the President and First Lady to run rampant on the platform.