On June 9, 2003, the U.S. Supreme Court said it will determine whether lower courts erred when they upheld a California air district’s regulations requiring diesel engine fleet operators in Los Angeles to purchase low-emission vehicles when replacing vehicles or expanding their fleet. Engine manufacturers, who failed to convince district and appeals courts that the South Coast Air Quality Management District violated the preemption provisions in the Clean Air Act, will argue that the “practical effect of the rule is that an air district is banning sales” of certain vehicles, thereby setting a standard that only state regulators have the authority to set. The requirements cover fleets of 15 vehicles or more in the area. The rules were challenged under a claim that they constituted new emission standards, thereby preempting federal standards. The National Association of Fleet Administrators, and the American Automobile Leasing Association submitted a brief in support of the Engine Manufacturers’ Association.