Automakers, car dealers and their allies still hope they can defeat a bill they say is a backdoor attempt at raising fuel economy standards - by the states instead of the federal government.
The bill, which would authorize California regulators to limit emissions of gases that may cause global warming, has been approved by the state Senate. The Assembly, which passed the measure in January, may consider the Senate changes this week.
Phil Isenberg, lobbyist for automakers, said the Assembly may reject the Senate version this time.
Sponsors have been careful to say they want to control emissions of carbon dioxide and other gases and not set fuel economy standards. Either way, the measure could be subject to a legal challenge on the grounds that the federal government has authority for fuel economy, opponents say.