Engine Manufacturers Association and Western States Petroleum Association v. South Coast Air Quality Management District

541 U.S. 246 · Decided April 28, 2004 · Supreme Court of the United States

At a glance

Engine Manufacturers Association and Western States Petroleum Association v. South Coast Air Quality Management District was decided on April 28, 2004 by a vote of 8–1. The Court vacated the lower court's decision and remanded the case. Justice Antonin Scalia wrote the opinion of the Court. SCDB classifies its main issue as “Federal preemption of state legislation or regulation” in the Federalism area.

Read the opinion

• CourtListener (Free Law Project) — opinion text
• Library of Congress — official U.S. Reports scan

Case details

How the Justices voted

Full case caption

Engine Manufacturers Association and Western States Petroleum Association v. South Coast Air Quality Management District et al.

SCDB identifiers: case 2003-050, docket 2003-050-01.

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Source: Supreme Court Database, 2026 Release 01 (data file dated September 8, 2026). Imported into CaseTrail November 5, 2026. Coverage: decisions from the 1946 through 2025 Terms. Methodology · Report an error