Lawyers at the  Knight First Amendment Institute have sent President Donald Trump a letter, Tuesday, arguing he is violating the First Amendment by blocking users on Twitter based on their views.

The letter also states Trump’s Twitter account which goes by the handle '@realDonaldTrump' is a “public forum” and hence the ban is unconstitutional.

Read: Donald Trump Twitter News: President To Continue Tweeting From Personal Account

The Knight First Amendment Institute, a non-profit under the Knight Foundation and Columbia University, represents several Twitter users who have been blocked from accessing Donald Trump's Twitter page after they wrote unflattering statements about the president.

The First Amendment, adopted on December 15, 1971, “prohibits the making of any law  respecting an establishment of religion, ensuring that there is no prohibition on the free exercise of religion, abridging the freedom of speech, infringing on the freedom of the press, interfering with the right to peaceably assemble, or prohibiting the petitioning for a governmental redress of grievances.”

“This Twitter account operates as a ‘designated public forum’ for First Amendment purposes, and accordingly the viewpoint-based blocking of our clients is unconstitutional,” the letter said. “We ask that you unblock them and any others who have been blocked for similar reasons.”

The Knight First Amendment Institute at Columbia University is representing several blocked Twitter users and has stated in its letter that if the Trump administration does not comply, a lawsuit will follow.

In the letter, the institute’s executive director, Jameel Jaffer said Trump did not have the right to exclude his critics from engaging with his posts.

One user, Joseph M. Papp, was blocked from Trump’s Twitter feed Sunday, after writing “Greetings from Pittsburgh, Sir” and “Why didn’t you attend your #PittsburghNotParis rally in DC, Sir? #fakeleader,” according to the letter.

While several critics have advocated for Trump claiming it is '@POTUS' that is the official account and not '@realDonaldTrump' making it legal for the president to block users from his personal account.

The lawyers’ correspondence comes after the administration confirmed Tuesday the president’s tweets should be taken as official statements, which support the lawyer's argument.

“The president is president of the United States," said White House Press Secretary Sean Spicer, "so they are considered official statements by the president of the United States."

"The president is the most effective messenger on his agenda and I think his use of social media ... gives him an opportunity to speak straight to the American people, which has proved to be a very, very effective tool,” Spicer added.

The lawyer’s letter further argued that “even if the space in question is 'metaphysical' rather than physical; even if the space is privately rather than publicly owned” the doctrine still applies especially since Trump has turned Twitter into the “official bull horn.” 

The president is known to respond to all major global events on Twitter. In the immediate aftermath of the recent London terror attack, Trump used the platform to pick a fight with London Mayor Sadiq Khan while also posting support for the U.K. after the attack.

He has even been seen criticizing tweets to other social media platforms, posting graphics of the tweets on Instagram or even celebrating longer tweet storms in videos uploaded to Trump's Facebook page.