Texas Attorney General Ken Paxton on Nov. 20 announced his office has launched an investigation into reporting conducted by liberal watchdog Media Matters. Media Matters has reported on Elon Musk and the social media platform he bought, X, which was formerly known as Twitter.

Now, according to reporting by NBC News, Media Matters has sued Paxton.

The lawsuit, filed Monday in a federal court in Maryland, characterizes Paxton’s investigation as unlawful retaliation that “chills their speech.”

Paxton’s investigation came after X sued Media Matters, alleging the watchdog manufactured a report showing advertisers’ posts alongside neo-Nazi and white supremacist posts.

The investigation prompted advertisers, including Disney and Apple, to pull ads from X.

X’s complaint claims the nonprofit “has manipulated algorithms governing the user experience on X to bypass safeguards and create images of X’s largest advertisers’ paid posts adjacent to racist, incendiary content, leaving the false impression that these pairings are anything but what they actually are: manufactured, inorganic and extraordinarily rare.”

Paxton referred to Media Matters as a “radical left-wing” organization.

The lawsuit, NBC News reports, asks a judge to block Paxton’s investigation permanently. It alleges First Amendment and 14th Amendment violations. The latter involves the guarantee of due process. The suit further alleges a violation of Maryland and Washington, D.C. “shield” laws that protect journalists from being compelled to disclose sources in some situations.

The lawsuit says that Paxton, a Republican, was one of several “politicians and media figures” who “swiftly jumped to Musk’s cause.”

Paxton’s office, as of Wednesday, has not publicly responded to the lawsuit.