Donald Trump. Pool/Getty Images The lawyers of two Twitter users whose accounts were blocked by President Donald Trump are demanding Trump unblock their clients, accusing the president of violating their First Amendment rights.

The @realDonaldTrump account blocked the two users this year after they posted tweets mocking and criticizing the president, the lawyers say.

"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 nonprofit Knight First Amendment Institute wrote in a letter to Trump on Tuesday.

"We ask that you unblock them and any others who have been blocked for similar reasons," it said.

One of the users cited in the letter, Holly O'Reilly, had her account blocked after posting a series of replies to one of Trump's tweets last month, according to the letter.

In one tweet, she promoted the March for Truth, an anti-Trump protest she said she helped organize. In another, she posted a GIF of Pope Francis appearing uncomfortable standing next to Trump, with the caption, "This is pretty much how the whole world sees you."

The other user, Joe Papp, was blocked for a tweet of his that contained the hashtag "#fakeleader," the institute said.

In a statement, Knight Institute executive director Jameel Jaffer acknowledged the uncharted legal territory his letter was entering.

"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," 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."

'You don't have a right to be listened to'

Donald Trump Win McNamee/Getty Images Whether the Knight Institute's argument would stand a chance in court is a matter for debate — and First Amendment attorneys are split on the issue.

Part of the issue hinges on whether Trump's personal social media account amounts to a government-designated public forum, like an open city-hall meeting. The Knight Institute said in its letter that its arguments also apply to the president's official @POTUS account.

"Frankly, I think that's somewhat of an open question that needs to be resolved by the courts," First Amendment lawyer Lisa Zycherman of Davis Wright Tremaine LLP told Business Insider.

"Once you become an elected official, your social media account is by an extension a forum for your constituents to engage with you," she said.

But Marc Randazza, a First Amendment lawyer with the Randazza Legal Group, said a president's social media account isn't a public forum, making the Knight Institute's argument meritless.

"I'm very expansionist when it comes to First Amendment rights," Randazza told Business Insider. "But this is a little bit of an overreach to say it's a First Amendment violation to block a critic on Twitter."

Randazza also countered the comparison of Trump's Twitter account to a town hall, opting for a different metaphor for the president's actions.

"If somebody was talking to him and he stuck his fingers in his ears and said, 'La la la, I'm not listening to you,' that's not a First Amendment violation either," he said.

"You don't have a right to be listened to. You have a right to speak," he said.

In a message to the Wall Street Journal, Ken Paulson, dean of media and entertainment at Middle Tennessee State University, called the Knight Institute's argument "novel and ambitious," but admitted it was "a tough sell" legally.

"I do think municipalities that establish Facebook pages and invite citizen input are in fact establishing public forums, but I’m not sure that Donald Trump’s brief bursts of opinion are the same thing," he said, according to The Journal.