An air-pollution district in metropolitan Los Angeles overstepped its authority when it enacted six "fleet rules" in 2000, the U.S. Supreme Court decided on April 28.

The rules prohibited public and private fleet operators from purchasing or leasing on-road vehicles that did not comply with local emission requirements that were more stringent than the federal Clean Air Act. The state’s South Coast Air Quality Management District also mandated use of "alternative" fuels, and banned use of diesel-powered vehicles.

Chicago-based Engine Manufacturers Association sued in 2000, arguing that the Clean Air Act supercedes local regulatory attempts. The district argued that it had procurement rules, not emissions standards. But the U.S. Supreme Court said that the district’s action "would undo Congress’ carefully calibrated regulatory scheme." The right of manufacturers "to sell federally approved vehicles is meaningless in the absence of a purchaser’s right to buy them," it added. The court remanded the case back to the federal district court for further action.

The decision has broader implications beyond the state and for off-road machinery, says Jed Mandel, EMA president. He calls the rules "a back-door attempt" to regulate emissions. A district statement claims the court "left the door open" for rules focusing on used equipment, leases and public procurement.