President Donald Trump’s executive order aiming to strip social-media companies’ protection from legal liability for speech on their platforms is unconstitutional, according to a lawsuit filed Tuesday by a nonprofit technology policy group.

The D.C.-based Center for Democracy & Technology filed a federal lawsuit naming Trump as a defendant “in his official capacity as President of the United States of America,” saying his executive order on “preventing online censorship” violates the First Amendment.

Trump — irate over Twitter’s move to append fact-checking labels to his inaccurate tweets about mail-in voting — issued an executive order May 28 that seeks to rescind legal immunity social networks have under current U.S. law if they “censor” speech.

The suit, filed in U.S. District Court for the District of Columbia, alleges that the executive order violates the First Amendment by curtailing and chilling the constitutionally protected speech of online platforms and individuals.

Trump’s executive order directs the FCC to craft new regulations under Section 230 of the 1996 Communications Decency Act that would remove the legal liability shield for social networks that “engage in censoring or any political conduct.” The law, as it currently stands, lets internet companies like Facebook, YouTube and Twitter moderate content on their services as they see fit, while protecting them from lawsuits over content shared on them.

In announcing the order last week, Trump complained that companies “like Twitter enjoy an unprecedented liability shield based on the theory that they are a neutral platform, which they are not.” His executive order also specifies that the administration withhold “taxpayer dollars” from social media companies that “repress free speech.”

In the lawsuit, CDT said that the processes prescribed by the order would “circumvent the role of Congress and of the courts in enacting and interpreting” Section 230 of the CDA. “The order clouds the legal landscape in which the hosts of third-party content operate and puts them all on notice that content moderation decisions with which the government disagrees could produce penalties and retributive actions, including stripping them of Section 230’s protections,” the lawsuit says.

CDT’s lawsuit seeks a declaration that Trump’s executive order “is unlawful and invalid,” as well as a preliminary and permanent injunction enjoining Trump and his administration from “implementing or enforcing any part of the Executive Order.” In addition, the suit seeks an order forcing Trump to pay CDT’s legal fees for the suit.

Donors to the Center for Democracy and Technology include Facebook, Twitter, Google, Apple and Amazon.

Twitter’s Public Policy team thanked CDT in a tweet, and reposted its comment from last week calling Trump’s executive order “a reactionary and politicized approach to a landmark law.”

Even with Trump’s attacks on Twitter, the company has vowed to continue fact-checking content on its platform. Last week, mere hours after the president issued the executive order, Twitter applied a warning label hiding a post by Trump about deploying force against protesters in Minneapolis that included the phrase “when the looting starts, the shooting starts”; Twitter deemed that as breaking its rules glorifying violence.

The situation has made things uncomfortable for Facebook CEO Mark Zuckerberg, who has defended his decision to leave the same Trump comments unchecked on Facebook and Instagram and reiterated in a Fox News interview last week that “it wouldn’t be right for us to do fact-checks for politicians.” Zuckerberg’s inaction on Trump’s inflammatory posts prompted public criticism from employees and a virtual walkout by several hundred staffers Monday.

The Trump executive order “is designed to deter social media services from fighting misinformation, voter suppression, and the stoking of violence on their platforms,” CDT president and CEO Alexandra Givens said in announcing the lawsuit. “Access to accurate information about the voting process and the security of our elections infrastructure is the lifeblood of our democracy.”

Givens continued, “The president has made clear that his goal is to use threats of retaliation and future regulation to intimidate intermediaries into changing how they moderate content, essentially ensuring that the dangers of voter suppression and disinformation will grow unchecked in an election year.”

Law firm Mayer Brown is representing CDT in the litigation.