A civil liberties group and seven people who have been blocked on Twitter by the president have filed a federal lawsuit in the Southern District of New York arguing that Donald Trump is violating the First Amendment by blocking dissenters on his @realdonaldtrump Twitter account.

In June, the Knight First Amendment Institute at Columbia University, which is one of the plaintiffs in the lawsuit, sent a letter to Trump asking him to unblock users who he blocked for criticizing him or his policies.

In the Knight Institute's letter to Trump, the organization threatened legal action on First Amendment grounds, claiming that being blocked on Twitter by the president "suppresses speech in a number of ways." A month later, Trump hasn't unblocked them, and so the Institute filed the lawsuit.

"Defendants' viewpoint-based blocking of the Individual Plaintiffs from the @realDonaldTrump account infringes the Individual Plaintiffs' First Amendment rights," the Knight Institute wrote in its complaint. "It imposes an unconstitutional restriction on their participation in a designated public forum"

Among the plaintiffs are Philip Cohen, a professor at the University of Maryland, and legal analyst and writer Rebecca Buckwalter. Cohen was blocked after tweeting a photo at the president with the words "Corrupt Incompetent Authoritarian. And then there are the policies. Resist." photoshopped onto it. Buckwalter was blocked after sending Trump a tweet saying that Russia had won him the White House.

The Knight Institute plans to argue that because Trump's administration has promoted his @realdonaldtrump account as a venue for official communication, it should be seen as a "public forum," like sidewalks and parks, which are protected under the First Amendment.

"The First Amendment applies to this digital forum in the way it applies to town halls and open school board meetings," Jameel Jaffer, the executive director of the Knight Institute, said in a statement emailed to Motherboard. "The White House acts unlawfully when it excludes people from this forum simply because they've disagreed with the president."

The lawsuit claims the rights of those who haven't been blocked are also being violated, because they're forced to participate in a forum that lacks the voices of those who Trump has blocked.

"A fundamental underpinning of the First Amendment is that you have the right to speak, and also that you have the right to hear," Katie Fallow, a senior attorney at the Knight First Amendment Institute told me on a phone call. "We wanted to make sure that we included that claim here because there's the danger that if government officials are allowed to sanitize or scrub forums of dissenting voices, it harms not just dissenters, but also those who want to hear what they have to say."

The Institute's argument is bolstered by last month's Packingham v. North Carolina Supreme Court decision, in which the court ruled that "cyberspace" is one of the most important places for "the exchange of views" in society today. Justice Anthony Kennedy specifically mentioned the importance of social media as a place for constituents to talk with elected officials. "On Twitter, users can petition their elected representatives and otherwise engage with them in a direct manner," he wrote in the opinion.

The ruling represents one of the first instances in which the court has decided on a case concerning free speech online. It's likely one of the most specific legal precedents the Knight Institute can use to strengthen their suit. Still, it doesn't provide a clear roadmap for everything that could happen in the lawsuit against Trump.

For example, it says nothing about what private companies like Twitter can or can't do: The company is still free to ban anyone who violates its terms of service and to moderate content however it wants. It could be tricky for the court to rule in a case where a public forum is potentially hosted by a private company, according to legal experts I spoke to last month.

A decision in the Knight case could also open the door for every elected official's social media account to be deemed a public forum, which could potentially lead to a cascade of related lawsuits in which citizens sue elected officials for blocking them on social media, the experts said.

"It creates a really difficult line-drawing argument," Neil Richards, a law professor at Washington University in St. Louis who specializes in the First Amendment told me when the case was decided last month. "It's trying to police a messy line between what is public and what is private."