Several Twitter users who have been blocked by President Donald Trump’s personal account ― they claim it was done because they criticized the president and his policies ― are now suing him in federal court. The lawsuit, filed Tuesday, argues that he violated the Constitution when he barred them.

The president’s personal Twitter account, @realDonaldTrump, is a “designated public forum” subject to the First Amendment, according to the suit brought by the Knight First Amendment Institute at Columbia University on behalf of itself and seven blocked Twitter users.

By cutting off the Twitter users allegedly because of their dissenting opinions, the suit contends that Trump has engaged in “viewpoint-based” discrimination in violation of the First Amendment.

The suit names the president as well as White House press secretary Sean Spicer and social media director Daniel Scavino as defendants. It was filed in the U.S. District Court for the Southern District of New York.

The president and his staff have “promoted” his personal Twitter account “as a key channel for official communication,” and his advisers have described Trump’s personal tweets as “official statements,” the lawsuit notes. The account is used to make formal announcements, defend the president’s actions and report the administration’s positions on various issues. The suit argues its operations are covered by the First Amendment.

The blocked Twitter users contend that their exclusion has “prevented or impeded [them] from viewing the President’s tweets, from replying to the tweets, from viewing the discussions associated with the tweets, and from participating in those discussions.” That violates both their rights and those of other Twitter users who haven’t been blocked, including the Knight First Amendment Institute, according to the lawsuit. The institute follows Trump’s account and argues that it has been deprived of its “right to read the speech of the dissenters who have been blocked.”

The suit requests that the court order the White House to restore the users’ access and ban the president from blocking others for the views they express.

The White House did not immediately respond to a request for comment on the lawsuit.

Last month, the Knight Institute sent a letter to Trump demanding that he unblock the Twitter users or they would take legal action. The White House did not unblock the accounts.

@realDonaldTrump Handout/Reuters

Legal experts do not agree on the novel First Amendment issues raised by the suit.

“I think it’s a close question,” Eugene Volokh, a free speech expert and professor of law at UCLA, told HuffPost, referencing two detailed Washington Post blog posts he’s written on the issue. “My tentative thinking has been that the lawsuit likely won’t prevail, but there have been some statements recently from the Administration that may suggest that @RealDonaldTrump is the account of Trump as officeholder, and not just Trump as politician, in which case the result might be different.”

Robert Loeb, a Washington lawyer who handles Supreme Court and other appellate litigation, supported the Knight Institute’s general arguments in a June post on the Lawfare blog. He compared the president’s Twitter page to a hypothetical government website with a comment section, which could be considered a designated forum for free speech and protected by the First Amendment.

“For the President to generally permit tens of thousands of comments on his posts on the @realDonaldTrump forum, but then selectively ban citizens from posting replies to his president’s posts based upon the content, message or viewpoint of the citizen appears to be clearly contrary to established First Amendment principles,” Loeb wrote.

Blocking someone’s Twitter account does not make it impossible for that person to view the president’s tweets, Loeb noted. But he argued it creates a “punitive barrier” that in this case was “based upon the viewpoint of the account holder” ― and that appears to violate the Constitution.

But another legal expert disagreed that the president’s personal Twitter account blocking another account is comparable to government censorship. Ken White, a criminal defense attorney in Los Angeles who writes on the law-oriented blog Popehat, told HuffPost that he didn’t find the lawsuit persuasive.

“It absolutely doesn’t prevent the person from posting whatever they want on Twitter and doesn’t impose any sort of civil or criminal penalty on them, nor substantively prevent them from petitioning the government,” White said. “This strikes me as part of the modern sentiment that we not only have a right to speak, but to make others listen to us. It’s a troll theory and I’m not a fan.”

The lawsuit “faces a pretty steep climb,” according to Ben Feuer, head of the San Francisco-based California Appellate Law Group.

“First, do you have a First Amendment right at all even to be on Twitter?” Feuer asked, noting that Twitter is a private company operating a private service that can and does ban individuals who post content that it deems unacceptable by its own subjective standards.

That said, some private places in the real world are deemed “quasi-public,” like airports and shopping malls, Feuer said, and limited First Amendment rights apply there.

“Second, if there is a First Amendment right to be on Twitter, does the President violate that right by blocking people who post things he doesn’t like from following his feed?” Feuer asked. “Third, is blocking someone from following you a violation of the First Amendment at all?”

He wondered whether the case would be different if @realDonaldTrump were an official government Twitter page that had banned users for posting negative statements.

The lawsuit certainly presents a “fascinating argument,” Feuer said.

“I think the Knight Institute is right,” Erwin Chemerinsky, the dean of the University of California, Berkeley, School of Law, told HuffPost.

He compared Twitter blocking to excluding reporters from receiving press credentials.

“Trump’s Twitter account is a way in which he communicates as president of the United States,” Chemerinsky said. “I see it no different than denying press credentials to those a government official dislikes.”

This story has been updated to include comment by Volokh.