The Federal Trade Commission announced a strange condition of the merger between two giant advertising companies. The FTC allowed the merger, but blocked the new company from being able to boycott media outlets based on political viewpoints.

The FTC announced Monday that Omnicom Group would be able to go ahead with its $13.5 billion purchase of The Interpublic Group of Companies. The merger faced antitrust concerns as the two companies are major players in the advertising industry. Currently, Omnicom is the third-largest ad agency in the United States, and IPG is fourth-largest.

Assuming the acquisition continues as planned, the enlarged Omnicom would be blocked from “engaging in collusion or coordination to direct advertising away from media publishers based on the publishers’ political or ideological viewpoints,” the FTC said.

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“Websites and other publications that rely on advertising are critical to the flow of our nation’s commerce and communication,” Daniel Guarnera, Director of the FTC’s Bureau of Competition, said. “Coordination among advertising agencies to suppress advertising spending on publications with disfavored political or ideological viewpoints threatens to distort not only competition between ad agencies, but also public discussion and debate. The FTC’s action today prevents unlawful coordination that targets specific political or ideological viewpoints while preserving individual advertisers’ ability to choose where their ads are placed.”

The new rule comes after Elon Musk, the owner of the social media platform X, formerly Twitter, complained that advertisers were boycotting the platform. Last August, X filed an antitrust lawsuit against the Global Alliance for Responsible Media, a coalition of advertisers, for boycotting X following Musk’s purchase of the company. Founding members of GARM include both Omnicom and IPG.

GARM was originally formed in response to the mass shooting in a Christchurch, New Zealand mosque by a white supremacist. The shooting was livestreamed on Facebook, and as such, advertisements appeared on the platform alongside the livestream. GARM aimed to block members’ advertisements from appearing on platforms that didn’t have safeguards prohibiting what the organization called “illegal or harmful content, such as promoting terrorism or child pornography.”

Days after the X lawsuit, GARM disbanded.

“GARM has disbanded under a cloud of litigation and congressional investigation. The Commission has not been a party to those actions, and I take no position on any possible violation of the antitrust laws by GARM. The factual allegations, however, if true, paint a troubling picture of a history of coordination—that the group sought to marshal its members into collective boycotts to destroy publishers of content of which they disapproved,” FTC Chairman Andrew N. Ferguson said Monday.

“GARM was neither the beginning nor the end of harmful and potentially unlawful collusion in this industry. Numerous other industry groups and private organizations have publicly sought to use the chokepoint of the advertising industry to effect political or ideological goals. Clandestine pressure campaigns and private dealings among these parties are less well documented but pose the serious risk of harm and illegality,” he added.

The proviso to the Omnicom merger is not the FTC’s only foray into this issue. This May, the FTC opened an investigation to determine whether or not advertisers coming together in agreement to not buy ads on certain websites due to political content constituted an illegal boycott, according to the New York Times.