Mayer Brown has filed a lawsuit against President Donald Trump on behalf of non-profit digital rights group Center for Democracy and Technology (CDT), alleging that his recent executive order to curtail the protection of social media giants such as Twitter violates the First Amendment, which protects freedom of speech.

The lawsuit alleges that President Trump’s executive order violates the First Amendment because it is “plainly retaliatory” and attacks a private company – Twitter – for exercising its right to comment on the President’s statements. The order was brought after Twitter added a fact-checking label to two of @realDonaldTrump’s tweets about California’s vote-by-mail plans to show where they could get ‘the facts’ – saying they believe the Tweets could confuse voters.

The lawsuit also alleges that the order breaches the First Amendment by seeking to “curtail and chill the constitutionally protected speech of all online platforms and individuals by demonstrating the willingness to use government authority to retaliate against those who criticise the government.” The order expressly names online content giants Twitter, Facebook, Instagram, and YouTube.

CDT is an organisation that promotes and protects free expression on the internet. It cites cases including New York Times Co. v Sullivan, which states that “The right of citizens to inquire, to speak and to use information to reach consensus is a precondition to enlightened self-government and a necessary means to protect it.”

The First Amendment prohibits government officials from using their power to retaliate against an individual or entity for engaging in free speech or take steps to chill free speech. It also bars the government from trying to censor lawful speech through threat of liability or reprisal. The claim alleges that the executive order violates all of these.

President Trump alleges the order defends free speech that a small number of powerful social media platform control a vast proportion of public and private communications. “They’ve had unchecked power to censor, restrict, edit, shape, hide and alter virtually any form of communication between private citizens or large public audiences,” adding that this has “no precedent in US history.”

He wants to revoke sector 230 of the Communications Decency Act 1996, which  protects the owners of any “interactive computer service” from liability for anything posted by third parties. President Trump says that section 230 gives big internet companies too much legal protection. While his order isn’t in itself legally enforceable and would take an act of Congress to enact, it is a threat and could be a deterrent on Twitter taking further steps to fact check the President’s tweets.

Ironically, if Section 230 is revoked, Twitter may have to take action against some of the more controversial posts from the President. Kate Ruane, senior legislative counsel at the American Civil Liberties Union, said: “Congress and the administration would do well to remember that Section 230 is critical to protecting free speech online. The law allows platforms to publish all sorts of content without fear of being held liable for it. That includes, as Donald Trump appears to have forgotten, his own tweets — even when they include lies.”

The lawsuit is being led for Mayer Brown by well-known litigation partner Andrew Pincus.