The Trump administration on Monday rejected an Obama-era plan to make automobiles more fuel efficient, opening up a long process to weaken current standards and putting California and the federal government on a collision course over vehicle emissions. Scott Pruitt, the administrator of the Environmental Protection Agency, said in a statement that the standards on the model year 2022 to 2025 vehicles were not appropriate and should be revised.

The Obama administration set the average fleet-wide fuel efficiency standards “too high” and “made assumptions about the standards that didn’t comport with reality,” Pruitt said. He did not offer specifics on revising them.The standards called for roughly doubling by 2025 the average fuel efficiency of new vehicles sold in the United States to about 50 miles (80 km) per gallon. Proponents said they could help spur innovation in clean technologies.California has long been allowed by an EPA waiver to impose stricter standards than Washington does on vehicle emissions of some pollutants. And 12 other states, including New York, Pennsylvania and Massachusetts, follow California’s lead on cleaner cars.

That has set up a battle on vehicle efficiency between California, the most populous U.S. state and a massive car market, and the administration of President Donald Trump.  Pruitt is a big proponent of states’ rights to regulate themselves but opposes California’s push for greener cars. California’s waiver to impose its own efficiency standards is being re-examined, the EPA said.