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Zachary Fayne concentrates his practice on environmental litigation and enforcement matters and regulatory counseling, with a particular emphasis on issues arising under the Clean Air Act, the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), and parallel California laws.

Zack's litigation practice focuses primarily on complex scientific and technical disputes, many of which involve complicated questions of constitutional law (including preemption and the First Amendment). He represents clients in business disputes, class action lawsuits, cost recovery actions, product liability and toxic tort litigation, and challenges to agency rulemakings. Zack also represents vehicle and engine manufacturers, consumer product manufacturers, and other diversified manufacturers in enforcement actions and investigations initiated by the U.S. EPA and California Air Resources Board (CARB) concerning alleged violations of the air quality regulations.

Zack regularly counsels clients regarding compliance with EPA and CARB air quality requirements, and has represented both businesses and trade associations in agency rulemaking proceedings. He also has advised numerous companies in connection with California's unique environmental and consumer protection laws, including Proposition 65, the Cleaning Product Right to Know Act, and the Home Furnishings and Thermal Insulation Act (relating to furniture flammability standards).

Zack has an active pro bono practice. Zack, together with co-counsel ArchCity Defenders and other Arnold & Porter attorneys, represents a class of individuals in Section 1983 lawsuits against several St. Louis municipalities alleging that the municipalities engage in unconstitutional debtors' prison practices to coerce payment of unpaid fines from traffic tickets and other minor ordinance violations. Zack also has partnered with the Washington Lawyers' Committee for Civil Rights and Urban Affairs in two Section 1983 lawsuits filed in federal district court related to the provision of inadequate medical care at an immigrant detention facility and excessive use of police force, respectively. Both cases resulted in favorable settlements, and Arnold & Porter received an Outstanding Achievement Award from the Washington Lawyers' Committee for its efforts.

Zack is a graduate of Harvard Law School, where he served as a Technical Editor of the Harvard Civil Rights-Civil Liberties Law Review. Prior to joining the firm, Zack worked at the Public Defender Service for the District of Columbia in the Special Litigation Division.


  • BP as part of a team of attorneys in litigation brought by the United States, citizen and environmental groups, states, and foreign governments arising from the Deepwater Horizon oil spill.
  • California Chamber of Commerce in federal court litigation challenging Proposition 65 warning requirement under the First Amendment.
  • Bayer Corporation, as national coordinating counsel, in personal injury litigation concerning Roundup-branded herbicides.
  • Fortune 500 company in litigation challenging on constitutional grounds the designation of a chemical as a carcinogen under Proposition 65.
  • Trade associations as amici curiae in series of lawsuits addressing federal preemption under Title II of the Clean Air Act.

  • Truck Trailer Manufacturers Association in successful challenge to U.S. EPA and NHTSA greenhouse gas and fuel economy standards for heavy-duty trailers.
  • Vehicle manufacturers in litigation challenging a rulemaking by CARB related to onboard diagnostics and recall authority.


Chambers USA
"Up and Coming" Environment (CA) (2023)
The Legal 500 US
Environment: Litigation (2022)
"Rising Star"—Environmental (2021)



  • J.D., Harvard Law School, 2009, cum laude
  • B.A., Washington University in St. Louis, 2006, summa cum laude


  • California
  • District of Columbia
  • Maryland
  • Supreme Court of the United States
  • U.S. Court of Appeals for the Ninth Circuit
  • U.S. Court of Appeals for the Fifth Circuit
  • U.S. District Court, District of Columbia
  • U.S. District Court, Northern District of California
  • U.S. District Court, Eastern District of California
  • U.S. District Court, Central District of California


  • Vice Chair, Section on Environment, Energy, and Resources, Air Quality Committee, American Bar Association
  • Member, Advisory Board, OneJustice