Elon Musk and X (formerly Twitter) are escalating their fight with the advertising industry, filing a federal antitrust lawsuit against a coalition the social media site says cost it billions of dollars in revenue.

The company has filed suit against the World Federation of Advertisers (as well as member companies Unilever, Mars, CVS Health, and Orsted) in federal court in Texas, saying an initiative by the group, called the Global Alliance for Responsible Media (GARM), coordinated an organized effort to stop advertising on the site after Musk took ownership of it.

“We tried being nice for 2 years and got nothing but empty words. Now, it is war,” Musk said in a posting on X.

Video-sharing platform Rumble, which hosts Truth Social and is popular with far-right users, has joined the suit, saying, “The brand safety standards set by advertisers and their ad agencies should succeed or fail in the marketplace on their own merits and not through the coercive exercise of market power,” in a statement.

X CEO Linda Yaccarino addressed the suit in a video on the platform as well, saying the Republican-led U.S. House Judiciary Committee had uncovered evidence that the GARM initiative had resulted in “a systematic illegal boycott.”

“People are hurt when the marketplace of ideas is undermined and some viewpoints are not funded over others as part of an illegal boycott,” she wrote in a follow-up open letter. “This behavior is a stain on a great industry, and cannot be allowed to continue.”

GARM was established in 2019 by the World Federation of Advertisers (WFA) to create standards for brand safety in digital advertising. Conservative media firms, led by the Daily Wire, alleged last month in Washington, D.C., that GARM was working with GroupM, a major ad-buying group, to discourage clients from buying ads on their sites. A Judiciary Committee report published just under a month ago suggested the group and its members “may have violated antitrust laws in their efforts to deprive conservative media outlets and personalities . . . of advertising dollars” (though no formal charges have been filed against GARM).