The company claimed that members of the Global Alliance for Responsible Media coordinated to dissuade brands from advertising on X.

X filed a lawsuit on Tuesday against the Global Alliance for Responsible Media, a coalition of major advertisers, claiming that it had violated antitrust laws by coordinating with brands to dissuade them from spending money on the social media platform.

The suit, filed in federal court in Texas, claims that the coalition, known as GARM, “conspired” with leading brands, including CVS, Unilever, Mars and the Danish energy company Orsted, to “collectively withhold billions of dollars in advertising revenue” that were owed to X, then known as Twitter, in the wake of Elon Musk’s takeover of the social media company in 2022.

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With the lawsuit, X effectively declared war on advertisers, which provide the bulk of the social media company’s revenue. Since Mr. Musk acquired the company and promised to usher in a new era of unfettered free speech, many advertisers have limited their spending on X, concerned by reports of rising hate speech and misinformation there. By pursuing legal action against GARM, Mr. Musk continued to break with the leaders of other social media companies, who have forged close relationships with advertisers and been responsive to their concerns about offensive online content.