The state of California has applied to the federal government for a waiver to let it implement the regulations under the Clean Air Act. Business interests led by a Central Valley car dealership and the Association of International Automobile Manufacturers sued the state. They claim the rule is a de-facto mandate on fuel-economy standards, which can be set only by the federal government. California, is the world's 12th-largest producer of greenhouse gases. The auto rules are designed to cut emissions from cars and light trucks by 25 percent and from sport utility vehicles by 18 percent beginning in 2009. A spokesman for Attorney General Jerry Brown said the state is awaiting the Supreme Court's decision. "We feel confident when that happens we'll be able to make the next step to enforcing the California law," spokesman Gareth Lacy said.

The Supreme Court is expected to rule later this year in a Massachusetts case about whether greenhouse gases should be regulated under the Clean Air Act. At a hearing in September, attorneys for the auto manufacturers said the technology did not exist to meet the California standards or could not be applied in a cost-effective way to cars sold in the United States. They argued the rules would increase the cost of vehicles and eliminate some types of trucks used by farmers.