Donald Trump is being sued because of his behaviour on Twitter.

The president's unprecedented Twitter use – which he has said is "modern day presidential" – has landed him a range of criticism in recent weeks. But the new lawsuit actually focuses not on his tweets but something else more private: his blocking critics on the site.

The new case argued that it is unconstitutional to stop people following him on Twitter. (Blocking people bans them from seeing your tweets or sending replies to them while signed into the blocked account.)

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The lawsuit has been filed in Manhattan and cites seven people who are no longer able to talk to or hear from their president because he or his aides have blocked him. As well as the president, Trump, the lawsuit also named as defendants White House Press Secretary Sean Spicer and Dan Scavino, White House director of social media.

Jameel Jaffer, the institute's director, said dozens of people reached out after his organisation told the White House three weeks ago that it wasn't permitted to block individuals from following the president's 8-year-old "realdonaldtrump" account.

Trump doesn't seem to be the only politician trying to limit his audience. Jaffer said numerous people have said they were blocked from the accounts of Republican and Democratic politicians after posting critical comments.

A federal judge in Washington, D.C., recently ruled that a local official's Facebook account was a public forum under the First Amendment, but higher courts have not yet addressed the issue, Jaffer said.

"It's fair to say that this is a new frontier," Jaffer said. "The First Amendment principle is well-settled, but the applicability of that principle to this context isn't an issue that the courts have yet had many occasions to address."

The lawsuit asks a judge to stop Trump and his media team from blocking critics from following his personal account, which has 33 million followers, 14 million more than (at)POTUS and 19 million more than (at)WhiteHouse.

Dawn Dearden, a spokeswoman for government lawyers, declined to comment.

According to the lawsuit, blocking people from following Trump's account was a viewpoint-based restriction the U.S. Constitution doesn't allow.

It noted that Trump on July 2 tweeted: "My use of social media is not Presidential — it's MODERN DAY PRESIDENTIAL." It also quoted Spicer saying a month earlier at a press conference that Trump's tweets should be understood as "official statements of the president of the United States."

Federal agencies and courts treat Trump's tweets as official statements, and The National Archives and Records Administration has advised the White House that the tweets must be preserved under the Presidential Records Act, the lawsuit said.

Among plaintiffs was Rebecca Buckwalter, a Washington-based writer and political consultant who was blocked from the account on June 6 after she replied to Trump's tweet saying he would have had "ZERO chance winning WH" if he'd relied on "Fake News" from major media outlets. Buckwalter received over 9,000 likes and 3,300 retweets after posting: "To be fair you didn't win the WH: Russia won it for you," according to the lawsuit.

Others to be blocked included Philip Cohen, a University of Maryland sociology professor who called Trump a "Corrupt Incompetent Authoritarian," and Holly Figueroa, a national political organizer and songwriter who was cut off May 28 after posting an image of the pope looking incredulously at Trump, along with the statement: "This is pretty much how the whole world sees you," the lawsuit said.