On May 29, 2026, the American Antitrust Institute (AAI) filed an amicus brief in FTC v. Meta Platforms, Inc., No. 26-5028, asking the D.C. Circuit to vacate a district court judgment in favor of Meta and remand for a proper analysis of the relevant market and Meta’s alleged monopoly power in the FTC’s Section 2 challenge to Meta’s acquisitions of Instagram and WhatsApp.
After a six-week bench trial, the district court ruled in Meta’s favor, finding that the FTC had failed to prove a relevant market for personal social networking services—centered on friends-and-family broadcast sharing—and that Meta lacked monopoly power even within the market the FTC alleged. The court placed dispositive weight on Meta’s experiments purporting to show diversion of consumer time between Facebook and Instagram on the one hand and TikTok and YouTube on the other, defining a broader market than the FTC alleged. It declined to find monopoly power based on Meta’s market shares, which the FTC’s expert calculated at between 54% and 62%.
AAI’s brief argues that the district court committed two independent categories of reversible error. First, it misapplied foundational market definition principles in four related but distinct ways. It bypassed analysis of functional interchangeability—whether consumers use TikTok and YouTube for the same purpose as Meta’s apps—and instead credited substitution evidence untethered from consumer purpose, effectively defining the market based on firms rather than products. It also misapplied the Hypothetical Monopolist Test because the evidence it relied on, including consumer behavior in response to temporary app outages and India’s permanent ban of TikTok, which modeled price increases ranging from 12% to infinity, did not properly approximate the small but significant and non-transitory price increase (SSNIP) the test requires. The court further failed to apply the “narrowest market principle,” which requires defining markets from the inside out rather than the outside in, and it drew the wrong inference from evidence of Meta’s sustained economic profits, which, properly understood, shows that TikTok and YouTube do not constrain Meta’s market power.
Second, the district court independently erred by applying an improper standard for measuring monopoly power. It treated a 65% market share as a de facto threshold for inferring monopoly power when the better-reasoned authorities hold that a market share above 50% can support a monopoly power finding. The FTC’s evidence cleared this threshold even in the district court’s overbroad market.
The brief was written by Brendan Benedict and Michael Altebrando of Benedict Law Group PLLC, a generalist litigation boutique with a focus on antitrust and consumer protection. AAI thanks Mr. Benedict and Mr. Altebrando for serving as pro bono counsel.
Read the full amicus brief: AAI Amicus Brief in FTC v. Meta Platforms, Inc.
