On November 8, the State of California filed a lawsuit against the U.S. EPA, claiming that the agency has "unreasonably delayed" action on California's request that EPA waive federal preemption of state regulations limiting vehicle emissions of greenhouse gases. Because vehicle emissions are regulated under the Clean Air Act, California’s more stringent emissions regulations could run afoul of federal law unless the EPA grants a preemption waiver. California filed its request for a waiver in December 2005.

California announced on April 25, 2007 that it would sue EPA if it did not act on the waiver within 180 days. In June, EPA announced that it would act on the waiver before the end of 2007.

Fourteen other states have intervened as plaintiffs in the lawsuit. These states and several others have adopted, or are considering adopting, vehicle emissions standards based on the California regulations. Their regulations would go into effect if and when EPA grants California's request for a waiver. However, in September a U.S. District Court in Vermont ruled that states could impose greenhouse gas emissions standards on automakers even without an EPA waiver.

State of California v. United States Environmental Protection Agency was filed in the United States District Court for the District of Columbia. Read the complaint here.