## Facts

- A California air-quality district adopted “Fleet Rules” applying to certain public and private fleet operators in the Los Angeles area.
- The rules prohibited covered operators from purchasing or leasing new vehicles that did not meet specified emissions-related criteria, effectively requiring acquisition of alternative-fuel or low-emission vehicles.
- Trade associations representing engine and fuel producers sued, alleging the rules were preempted by Clean Air Act (CAA) § 209(a), which bars state and local entities from adopting or attempting to enforce “any standard relating to the control of emissions from new motor vehicles or new motor vehicle engines.”
- The district court granted summary judgment for the air-quality district, concluding the rules were not “standards” because they regulated purchasers of already-certified vehicles rather than manufacturers or sellers.
- The Ninth Circuit affirmed on the same reasoning.

## Issues

1. Whether CAA § 209(a) preempts local regulations that restrict the purchase or lease of new vehicles by requiring specified emissions characteristics.
2. Whether a purchase mandate can constitute an “attempt to enforce” a “standard relating to the control of emissions” even if it does not directly regulate manufacturing or sales.

## Decision

- The Supreme Court, in an 8–1 opinion by Justice Scalia, held that purchase and lease restrictions can qualify as preempted “standards” or as “attempt[s] to enforce” such standards under CAA § 209(a).
- The Court rejected the view that “standard” is limited to manufacturer-directed production requirements, treating that distinction as confusing standards with enforcement mechanisms.
- The Court vacated the Ninth Circuit’s judgment and remanded for further proceedings, leaving open how preemption applies to any provisions that might reflect government purchasing as a market participant rather than regulation of private purchasers.

## Legal Principles

- Under CAA § 209(a), a “standard” refers to criteria tied to a vehicle’s or engine’s emissions characteristics, not merely to the identity of the regulated actor.
- A command that certain purchasers may buy or lease only vehicles with particular emissions characteristics can be an “attempt to enforce” an emissions standard and is subject to § 209(a) preemption.
- State and local governments may not evade § 209(a) by imposing emissions-characteristic requirements through procurement mandates that functionally replicate prohibited new-vehicle standards.
- Preemption analysis may differ where a government entity is acting as a market participant in its own purchasing, an issue not resolved and left for consideration on remand.

## Conclusion

The Court held that local fleet rules restricting purchases of new vehicles based on emissions characteristics can be preempted by Clean Air Act § 209(a) as standards, or attempted enforcement of standards, and it vacated and remanded for further proceedings, including consideration of any market-participant applications.


Engine Mfrs. Ass'n v. S. Coast Air Quality Mgmt. Dist., 541 U.S. 246 (2004)