Apart from the man himself, perhaps nothing has defined President Donald Trump’s political persona more than Twitter.

But on Wednesday, one of Trump’s Twitter habits — his practice of blocking critics on the service, preventing them from engaging with his account — was declared unconstitutional by a federal judge in Manhattan.

Judge Naomi Reice Buchwald, addressing a novel issue about how the Constitution applies to social media platforms and public officials, found that the president’s Twitter feed is a public forum. As a result, she ruled that when Trump or his aides blocked seven plaintiffs from viewing and replying to his posts, they violated the First Amendment.

If the principle undergirding Wednesday’s ruling in U.S. District Court stands, it is likely to have implications far beyond Trump’s feed and its 52 million followers, said Jameel Jaffer, the Knight First Amendment Institute’s executive director and the counsel for the plaintiffs. Public officials throughout the country, from local politicians to governors and members of Congress, regularly use social media platforms like Twitter and Facebook to interact with the public about government business.

“This ruling should put them on notice, and if they censor critics from social media accounts used for official purposes, they run the risk that someone will sue them and win,” he said of public officials.

Asked whether the administration would unblock the users or appeal the ruling, Kerri Kupec, a spokeswoman for the Justice Department’s civil division, demurred from making any specific pronouncement. “We respectfully disagree with the court’s decision and are considering our next steps,” she said.

In her ruling, Buchwald said Trump and Dan Scavino, the White House social media director, “exert governmental control over certain aspects of the @realDonaldTrump account.”

But she did not issue an injunction ordering Trump or Scavino to unblock the users, a nod to the separation-of-powers sensitivities of a judge’s ordering a president to do something. Rather, her ruling simply declared what the Constitution requires, with the expectation that the White House would comply.

“Because no government official is above the law and because all government officials are presumed to follow the law once the judiciary has said what the law is, we must assume that the president and Scavino will remedy the blocking we have held to be unconstitutional,” she wrote in her ruling.

The plaintiffs had argued that Trump’s Twitter feed is an official government account and that blocking users from following it is a violation of their First Amendment rights.

In June, the plaintiffs sent a letter to the White House asking to be unblocked. When that went ignored, they sued.

Their complaint argued that Trump’s feed amounted to a “digital town hall” where not only did the president and his aides communicate information but members of the public — by replying to Trump’s tweets and others who responded to him — exchanged views with one another. By blocking particular people from viewing or replying to message chains because they had expressed views he did not like, it argued, Trump had violated their First Amendment rights.

Buchwald, who was appointed to the federal bench in 1999 by President Bill Clinton, agreed.

“The viewpoint-based exclusion of the individual plaintiffs from that designated public forum is proscribed by the First Amendment and cannot be justified by the president’s personal First Amendment interests,” she wrote.

The ruling also rejected the government’s claim that Trump operates the account merely in a personal capacity, concluding that he “uses the account to take actions that can be taken only by the president as president.”