President Donald Trump’s order targeting social media companies was challenged in court by a non-profit group that claims the edict violates free-speech protections guaranteed by the First Amendment.

Trump’s order, issued on Thursday, might undermine the legal protections enjoyed by social media companies including Twitter and Facebook. He asked federal regulators to look at provisions, contained in Section 230 of the 1996 Communications Decency Act, that insulate the companies from liability for content posted by users.

The order followed on the heels of Twitter’s decision to add fact-check labels to two of Trump’s tweets. Twitter also restricted a post by the president suggesting that protesters who engaged in looting would be met with violence. Legal observers have said Trump lacks the power to modify Section 230 by executive order.

The Center for Democracy and Technology sued in Washington federal court Tuesday, claiming the order is an unconstitutional retaliation against Twitter and that it seeks to discourage other companies and individuals from disagreeing with the government.

The case is Center for Democracy and Technology v. Trump, 20-cv-01456, U.S. District Court, District of Columbia (Washington).