“Undeterred by the truth, Media Matters has opted for new tactics in its campaign to drive advertisers from X,” claimed the site once known as Twitter.

Elon Musk’s X sued the watchdog group Media Matters for America for defamation on Monday after the nonprofit published a report about ads for major brands appearing alongside posts touting Nazism.

Media Matters first published details Thursday about the spread of Nazi-related content on the social media platform, formerly known as Twitter, saying X had been placing ads for major brands, including Apple, IBM and Comcast’s Xfinity, next to offending content. The research group published screenshots of posts praising Hitler that ran adjacent to the ads shortly after Musk seemed to endorse an antisemitic conspiracy theory on the site.