Elon Musk's X has lost tons of advertisers. The platform's solution is to sue them.

• X is suing a group of advertisers, alleging they violated antitrust law.
• The suit alleges an advertising group persuaded top brands to withhold billions in ad revenue from X.
• X CEO Linda Yaccarino said the boycott undermined the marketplace of ideas.

Elon Musk's X is suing a group of advertisers, alleging that they violated antitrust laws by ganging up on the social-media company in an advertising boycott.

X CEO Linda Yaccarino posted a video and an open letter on the platform Tuesday announcing the lawsuit against the Global Alliance for Responsible Media, the World Federation of Advertisers, and the GARM members CVS Health, Mars, Ørsted, and Unilever.

The lawsuit, filed in Texas, says that after Musk took over the platform in 2022, GARM persuaded top brands not to advertise on X in an effort to "collectively withhold billions of dollars in advertising revenue" from the platform, The New York Times reported .

"The consequence - perhaps the intent - of this boycott was to seek to deprive X's users, be they sports fans, gamers, journalists, activists, parents or political and corporate leaders, of the Global Town Square," Yaccarino wrote in the letter. "To put it simply, people are hurt when the marketplace of ideas is undermined and some viewpoints are not funded over others as part of an illegal boycott."

Musk also weighed in on the lawsuit in several posts on X.

"I strongly encourage any company who has been systematically boycotted by advertisers to file a lawsuit," Musk wrote in one post . "There may also be criminal liability via the RICO Act."

In another, Musk shared Yaccarino's message, writing: "We tried peace for 2 years, now it is war."

A representative for GARM and the WFA did not immediately respond to a request for comment.

Since Musk took over the platform (formerly Twitter) and began reshaping it — slashing its moderation team, laying off workers, and declaring the platform a haven of "free speech" — advertisers have fled, dealing a crippling blow to X's advertising revenues.

The advertisers left after critics noted antisemitic and hateful rhetoric on the platform.

Documents obtained by Bloomberg showed X lost roughly 40% of its revenue in the immediate aftermath of the takeover.

Musk, for his part, has gone on offense. He infamously told advertisers that had left his platform to go "fuck" themselves in November.

Since then, he's tried to woo advertisers back . It's not clear that'll work, Business Insider's Peter Kafka wrote last month.

His return to aggression against advertisers who want out is mirroring a push by Republican lawmakers to investigate Musk's advertising opponents .

The GOP-led House Judiciary Committee stepped up its investigation of GARM earlier this year, sending out subpoenas as part of an inquiry into allegations of anti-conservative bias.

A spokesperson for the committee said in May: "These companies know the evidence collected shows that members of GARM have worked for years to spread their personal biases and censor conservative voices and journalists online."

Several people close to the companies, meanwhile, told BI's Lara O'Reilly that they were concerned the allegations and investigations would intensify during an election year.

Another advertising-industry veteran said the inquiries would have a "chilling effect."