US President Donald Trump and high-ranking members of the White House staff were sued yesterday by America's Knight First Amendment Institute, which alleges the president's blocking of dissenting Twitter users violates the Constitution.
The case filed in Manhattan federal court seeks a court order that Mr Trump stop the practice.
The institute, a non-profit organisation affiliated with Columbia University, first warned it might seek an injunction in early June when it sent a letter to Mr Trump, his counsel, press secretary, and social media director.
At the time, the institute represented two Twitter users, both of whom said they were blocked after criticising Mr Trump.
Yesterday's lawsuit represents seven users. In the complaint, the foundation argued that the president's Twitter account, @realDonaldTrump, was "a public forum under the First Amendment" because of how Mr Trump and his staff used the account to communicate.
Press secretary Sean Spicer previously said Mr Trump's tweets were official statements. "President Trump's Twitter account has become an important source of news and information about the government, and an important forum for speech by, to, or about the president," Jameel Jaffer, the institute's executive director, said.
"The First Amendment applies to this digital forum in the same way it applies to town halls and open school board meetings.
The White House acts unlawfully when it excludes people from this forum simply because they've disagreed with the president."
The Knight Institute requested that the court move to declare "viewpoint-based blocking" by the president's account unconstitutional, unblock the plaintiffs, and pay the plaintiffs' attorney fees. A request for comment from the White House wasn't immediately returned.
One plaintiff, comedian Nick Pappas, said he was blocked after replying to a tweet the president wrote about travel ban litigation.
"Trump is right. The government should protect the people. That's why the courts are protecting us from him," Mr Pappas tweeted.
He said he was blocked the day of his post, which got hundreds of retweets. Eugene Gu, another plaintiff, said he was blocked about two hours after tweeting at Mr Trump: "Covfefe: the same guy who doesn't proofread his Twitter handles the nuclear button." Trump had tweeted, and then deleted, a post including the mysterious word "covfefe".