Elon Musk’s X has accused a group of major advertisers of antitrust violations in a new lawsuit claiming the group conspired to “boycott” advertising on the platform.

The lawsuit claims an influential ad industry group organized “to collectively withhold billions of dollars in advertising from Twitter” because the group was concerned that the platform had deviated from brand safety standards after Musk’s acquisition in late 2022.

The group is the Global Alliance for Responsible Media, also known as GARM, a voluntary ad-industry initiative run by the World Federation of Advertisers that aims to help brands avoid having their advertisements appear alongside illegal or harmful content.

GARM counts more than 100 prominent companies as members. Four of those companies — CVS, Unilever, Mars and the Danish energy company Ørsted — were also named as defendants in the lawsuit, which was filed in federal court in Texas Tuesday.

The lawsuit is the latest effort by X to revive its core ad business, which has tanked since Musk’s takeover. Many brands have pulled their spending over concerns that their ads might run alongside misinformation or hate speech, which Musk himself has occasionally promoted.