A top California environmental regulator is threatening to enact tough, new pollution rules — including an unprecedented ban on cars burning petroleum-based fuels — in response to a Trump administration plan to relax vehicle emission standards.

California Air Resources Board Chairman Mary Nichols said the state would be forced to pursue “extreme” requirements to offset the uptick in pollution that would be unleashed if federal vehicle emission and fuel economy standards are weakened.

“If we lose the state vehicle standards, we have to fill up the gap with other measures,” Nichols said at a forum on the issue Thursday. “We will be faced with dramatic alternatives in terms of tighter, stricter controls on everything else, including movement of vehicles and potentially looking at things like fees and taxes and bans on certain types of vehicles and products.”