Antitrust Law Daily Wrap Up, ANTITRUST NEWS: DOJ backs X Corp. in Fifth Circuit advertising boycott appeal, arguing district court conflated antitrust injury with the merits, (Aug 18, 2026)

By Wendy Biddle, J.D.

The DOJ contends that the lower court applied the wrong legal framework at every step of its analysis.

The United States Department of Justice has entered the Fifth Circuit appeal of X Corp. v. World Federation of Advertisers as amicus curiae in support of X Corp., arguing that the Northern District of Texas committed two distinct legal errors when it dismissed X's Sherman Act claims against a group of major advertisers and the global marketing organization that coordinated their conduct to boycott advertising on the platform. The brief takes no position on whether X will ultimately prevail on the merits but contends that the district court's reasoning was wrong as a matter of law. The American Antitrust Institute and a coalition of twelve Republican-led states also joined the fray with their own amicus briefs (X Corp. v. Mars, Inc., No. 26-10394 (5th Cir. Aug. 12, 2026)).

Background. X Corp., the company that operates the social media platform formerly known as Twitter, filed suit against a group of corporate advertisers as well as the World Federation of Advertisers (WFA). X alleged that the defendants coordinated an advertising boycott through GARM, the Global Alliance for Responsible Media, a body founded in 2019 by WFA and certain of its members to leverage their collective purchasing power over digital and social media platforms.

According to X's Second Amended Complaint, GARM promulgated Brand Safety Standards governing the display of sensitive content on digital platforms, along with techniques for implementing those standards and common metrics for measuring compliance. Before GARM's formation, individual advertisers had negotiated separately with each platform to avoid unwanted content adjacency, and acting unilaterally they lacked the collective leverage to compel platforms to adopt uniform standards. GARM was designed to change that dynamic.

When Elon Musk acquired Twitter in 2022, WFA expressed concern that the acquisition would result in Twitter departing from GARM's Brand Safety Standards. WFA and GARM then triggered a boycott, with the publicly stated condition being that Twitter must implement and adhere to those standards to WFA members' satisfaction as a condition of receiving their advertising business. Advertising agency members of GARM issued recommendations to their clients to suspend paid advertising on Twitter, and those recommendations were widely followed. By late 2022, at least eighteen GARM-member advertisers had stopped purchasing advertising from Twitter entirely, and dozens more substantially reduced their spending, in many cases by more than seventy percent. X alleged that the boycott continues to the present day.

X brought claims under Section 1 of the Sherman Act for a continuing group boycott and an unlawful information exchange.

District court's dismissal. The district court dismissed the complaint on the ground that X had failed to establish antitrust injury, which is a threshold component of private antitrust standing, and denied leave to amend. The district court held that an illegal group boycott must involve a competitor seeking to restrain competition against an outsider to the agreement, and that because the defendants are advertisers rather than competing social media platforms, X's allegations could not satisfy that requirement. The court analyzed two possible theories: whether the defendants' conduct allowed a competitor to corner the supply of online advertising space; and whether it restrained X from selling to downstream customers, and found both wanting. It concluded that no antitrust violation had been alleged and dismissed with prejudice. Later, WFA and X jointly announced that the companies had reached an agreement to drop WFA from the dispute.

DOJ's arguments. In its amicus brief, the DOJ identifies two independent errors in the district court's analysis.

First, the DOJ argues that the district court improperly merged the antitrust injury inquiry with the merits. Under controlling Fifth Circuit precedent, antitrust injury is meant to function as a quick threshold screen, one that weeds out claims of injury flowing from increased rather than decreased competition, not as a vehicle for resolving whether the plaintiff has adequately pled a substantive violation. The proper method, which the Fifth Circuit has articulated repeatedly, is for a court to assume the existence of an antitrust violation and then ask whether the plaintiff's alleged injuries flow from that assumed violation.

The district court did the opposite, the DOJ argues. Rather than assuming a boycott and examining whether X's injuries were proximately caused by it, the court determined that X had not adequately alleged a boycott and then reasoned backward to conclude that X had not suffered antitrust injury. The DOJ argues this approach is both incorrect and inefficient, citing the Fifth Circuit's own admonition in Doctor's Hospital of Jefferson, Inc. v. Southeast Medical Alliance, Inc., 123 F.3d 301 (5th Cir. 1997), that found requiring a plaintiff to establish substantive violations as a prerequisite to antitrust injury is "inefficient and confusing."

Under the proper framework, the DOJ contends, X's alleged injuries plainly satisfy the antitrust injury standard. X sells advertising space, and it is the immediate victim of the alleged concerted refusal to purchase. Its injuries flow directly from the competition-suppressing effect of major advertisers agreeing to stop competing with one another for inventory on X's platform. The DOJ further argues that X's injuries are of the type the antitrust laws are designed to prevent because the alleged boycott is an attempt to use collective rather than competitive pressure to dictate the quality standards of X's product, precisely the kind of collusion the Sherman Act is intended to displace.

Second, the DOJ argues that the district court applied an unduly narrow conception of what conduct can constitute a group boycott. The court appeared to require either that a competitor of X orchestrated the boycott or that third parties were coerced into refusing to deal with X. The DOJ argues no such rigid rule exists. The DOJ notes that in the Fifth Circuit group boycotts have long been recognized in three categories, the third of which encompasses combinations designed to influence the trade practices of the boycott victim rather than to eliminate it as a competitor. The Fifth Circuit held in Tunica Web Advertising v. Tunica Casino Operators Association, 496 F3d 403 (5th Cir. 2007), that "nothing in Northwest Wholesale Stationers or the Supreme Court's later cases establishes a bright-line rule limiting the application of the per se rule to cases in which the victim is a competitor of at least one of the conspirators."

The DOJ also faults the district court for failing to consider two additional theories that X's complaint plausibly supports. The first is a monopsony theory. X alleges that the defendant advertisers collectively exercise monopsony power in the market for digital advertising and that their coordinated refusal to purchase advertising deprived X of a critical input, advertising revenue, which comprises approximately ninety percent of the platform's revenue. The DOJ argues this is a cognizable group boycott theory under both the per se rule and the rule of reason, consistent with longstanding precedent holding that collusive buyer conduct is subject to the same antitrust scrutiny as collusive seller conduct.

The second overlooked theory is one based on the concerted enforcement of a private product quality standard. The DOJ notes that GARM and its members not only formulated the Brand Safety Standards but also agreed to enforce them against X. Concerted enforcement of private product standards, the DOJ argues, faces more rigorous antitrust scrutiny than mere agreement on standards, and X's complaint contains sufficient allegations to support a claim on that basis.

Relief sought. The DOJ asks the Fifth Circuit to hold that the district court erred in its antitrust injury analysis, that a group boycott need not be directed by a competitor of the victim, and that the case presents viable boycott theories beyond the two the district court considered.

Additional amicus filings. Two other groups weighed in and also filed amicus briefs. The American Antitrust Institute, a nonprofit competition advocacy organization, filed a brief supporting neither side but urging the Fifth Circuit to clarify a legal distinction it says the district court badly muddled. The AAI argues that the lower court improperly conflated two separate legal questions: whether X has standing to bring an antitrust claim (the "antitrust injury" doctrine), and whether X actually stated a valid antitrust claim on the merits. According to the AAI, the district court's dismissal was analytically incoherent. It used X's failure to plead a viable antitrust violation as the basis for denying antitrust standing, when those are distinct inquiries governed by different legal standards. The AAI takes no position on whether X should win, but insists the Fifth Circuit needs to set the record straight on how these doctrines properly work.

A coalition of twelve Republican-led states, led by West Virginia, filed a brief squarely backing X and urging reversal of the district court's dismissal of several foreign defendants for lack of personal jurisdiction. The states argue that the district court wrongly imported the Fourteenth Amendment's "minimum contacts" framework, which limits state courts, into a federal case governed by the Fifth Amendment; even after the Supreme Court's 2025 decision in Fuld v. Palestine Liberation Organization, 606 U.S. 1 (2025), made clear those standards diverge. The states further contend that the district court misread Section 12 of the Clayton Act, which authorizes nationwide service of process in antitrust cases, in a way that improperly shielded foreign defendants like Ørsted from suit. The brief emphasizes that narrowing federal court jurisdiction over foreign antitrust defendants ultimately harms states and their citizens, who often have no other forum to seek relief against foreign wrongdoers.

The Case is No. 26-10394.

Attorneys: Paul D. Clement (Clement & Murphy, P.L.L.C.) for X Corp. Karen Mary Lent (Skadden, Arps, Slate, Meagher & Flom, L.L.P.) for Mars, Inc.

Companies: X Corp.; Mars, Inc.

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