Lawyers for Twitter users blocked by Trump after they criticized or mocked him are asking him to reverse the moves https://t.co/CkY42LPnzp pic.twitter.com/tID5Q58uHh

— NYT Politics (@nytpolitics) June 6, 2017

WASHINGTON — Lawyers for Twitter users blocked by President Trump after they criticized or mocked him are asking him to reverse the moves, arguing that the Constitution bars him from blocking people on the social media service.

The request raises novel legal issues stemming from Mr. Trump’s use of his Twitter account, @realdonaldtrump, to make statements about public policy. In a letter sent to Mr. Trump on Tuesday, lawyers for several users he has blocked argued that his account was a “public forum” from which the government may not constitutionally exclude people because it disagrees with views they have expressed.

“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 letter implies that if the Trump administration does not comply, a lawsuit may follow. The blocked Twitter users are represented by the Knight First Amendment Institute at Columbia University, whose executive director, Jameel Jaffer, said in a statement that Mr. Trump did not have a right to exclude his critics from engaging with his posts.

“Though the architects of the Constitution surely didn’t contemplate presidential Twitter accounts, they understood that the president must not be allowed to banish views from public discourse simply because he finds them objectionable,” Mr. Jaffer said. “Having opened this forum to all comers, the president can’t exclude people from it merely because he dislikes what they’re saying.”