President Donald J. Trump can’t block Twitter users from following his personal account, a federal judge ruled.

The judge said the comment section of Trump’s personal account, @realDonaldTrump, is a public forum and that blocking users on the basis of political speech is a violation of their free-speech rights under the First Amendment.

U.S. District Judge Naomi Reice Buchwald in Manhattan issued the ruling Wednesday in a lawsuit brought by the Knight First Amendment Institute at Columbia University on behalf of seven Twitter users who were blocked by Trump after replying to his tweets.

“This case requires us to consider whether a public official may, consistent with the First Amendment, ’block’ a person from his Twitter account in response to the political views that person has expressed, and whether the analysis differs because that public official is the President of the United States,” Buchwald said. “The answer to both questions is no.”

The judge declined to issue an order forcing Trump to unblock the users, saying her ruling should be sufficient to force a change in behavior.

The case is Knight First Amendment Institute v. Trump, 17-cv-5205, U.S. District Court, Southern District of New York.