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).

Musk took that accusation even further, writing, “there may also be criminal liability via the RICO Act” [a law that targets organized criminal activity and racketeering] in his plea for other companies to file their own lawsuits against GARM.

WFA and GARM did not immediately respond to Fast Company’s request for comment about the suit.

The X court action appears to be a SLAPP (Strategic Lawsuit Against Public Participation) lawsuit, which is a legal action meant to silence or intimidate critics by making them bear the cost of legal defenses, which can become so burdensome that the group abandons its criticism. Musk urged “everyone who has ever been boycotted” to file their own suit “in every country they’ve been boycotted.”

Prior to Tuesday’s suit, X has also sued Media Matters, alleging the group misrepresented the likelihood that users may encounter hate speech on the social media site. That case will go to court next April. Musk, last November, also said he hoped advertisers who had left would stop advertising on the platform, adding, “If someone is trying to blackmail me with advertising—blackmail me with money—go fuck yourself.”

A separate suit by X against an anti-hate group was dismissed earlier this year, with the judge saying the legal action was designed to punish speech.

GARM, on its website, says it is an apolitical group, that allows members to determine what content is suitable to their companies.

“GARM does not look at harmful content or content risk through a political lens, nor does it advocate doing so,” the organization wrote. “Suggestions that GARM practices may impinge on free speech are a deliberate misrepresentation of GARM’s work. GARM is not a watchdog or lobby. GARM does not participate in or advocate for boycotts of any kind.”

The group added it is not involved in any decisions related to the allocation of advertising budgets and does not interfere with members’ decisions on where to advertise.

Other members of the group include Disney, Coca-Cola, American Express—and, according to the group’s website, X.