Musk sued the liberal nonprofit in 2023 after it published a report that showed mainstream ads appearing beside pro-Nazi content on his social media site X.

The probe marks an escalation in U.S. government scrutiny of whether groups like Media Matters helped advertisers coordinate to pull ad dollars from X.

The New York Times reported that the Federal Trade Commission launched an investigation into Media Matters over alleged collusion with advertisers against Elon Musk's X.