Matthew Diehr

Overview Matt leads the firms State Attorneys General Practice, focusing his practice primarily on representing clients in high-stakes antitrust and commercial litigation matters, and in civil and criminal investigations and litigation brought by State Attorneys General and the federal government. Matt concentrates his practice on representing clients facing enterprise-threatening commercial litigation, defending clients and their businesses in state and federal courts across the country. He has a successful track record at trial and is known as a talented writer who can win a case through dispositive motion practice. As co-founder and leader of the firms State Attorneys General group, Matt has also built a national practice that has grown alongside client needs. He frequently interfaces with State Attorneys General across the country, advocating for clients on important policy positions and cases of national importance and supporting clients through sensitive litigation, antitrust matters, and multi-state investigations and regulatory enforcement matters brought by State Attorneys General. Matt routinely represents clients facing scrutiny from the Federal Trade Commission and DOJ Antitrust, both in the context of merger review and conduct investigations. Matts recent successes include: Counseled clients applying for and receiving corporate leniency from DOJ Antitrust. No criminal charges were filed against the client. Represented GKN Aerospace Inc. and parent Melrose Industries in complex commercial dispute with The Boeing Company in St. Louis County Court and United States District Court for the Eastern District of Missouri. The matter was resolved with a confidential settlement. Represented clients investigated by DOJ Antitrust in alleged wage-fixing conspiracy. No criminal charges were filed against the client. Represented an agricultural coalition that obtained preliminary injunction against enforcement of Californias Proposition 65 warning requirement on First Amendment grounds; case currently stands as the only time a federal court has enjoined a Proposition 65 warning requirement on First Amendment grounds. Represented client facing scrutiny of Federal Trade Commission and DOJ Antitrust relative to merger review investigations of alleged violations of the antitrust laws. Represented a high-ranking executive in the telecommunications industry accused of conspiracies to commit wire fraud, mail fraud, and money laundering. United States vs. Pajaczkowski, S. D. N. Y., 15-cr-606. Despite sentencing guidelines suggesting 20-25 years of incarceration, the client was sentenced only to time served. As first-chair trial counsel, obtained sizable jury verdict for compensatory damages in U. S. District Court, Eastern District of Missouri. Represented a medical provider in complex commercial litigation matters in federal court involving allegations of violations of the antitrust laws, Sherman Act sections 1 and 2. Industries Manufacturing Technology Transportation Services Antitrust & Competition Antitrust Litigation Appellate False Claims Act Litigation & Alternative Dispute Resolution State Attorneys General Practice White Collar, Internal Investigations, & Compliance Recognition The Best Lawyers in America Appellate Practice, 2024-2026 Benchmark Litigation Future Star, 2026 40 & Under List, 2023 and 2024 Missouri Lawyers Media, POWER List for White Collar Defense, 2020-2022 Missouri & Kansas Super Lawyers, Litigation, Rising Star, 2018-2019 Education J. D., Saint Louis University School of Law B. A., Tulane University Admissions Missouri U. S. District Court, Eastern District of Missouri U. S. District Court, Western District of Missouri Illinois U. S. District Court, Southern District of Illinois U. S. District Court, District of Kansas U. S. District Court, District of Colorado U. S. Court of Appeals, Eighth Circuit U. S. Court of Appeals, Ninth Circuit U. S. Court of Appeals, Tenth Circuit Professional Memberships and Certifications Federal Bar Association, St. Louis Chapter, Former President Bar Association of Metropolitan St. Louis