Environmentalists are deeply concerned about the Trump administration’s proposed rollback of previously-established fuel efficiency and emissions standards. The EPA and the National Highway Traffic Safety Administration have released a new proposed rule that would freeze fuel economy standards for new vehicles at their 2020 levels for six years instead of allowing them to ratchet up over time. Public comment on the proposal will be open for 60 days, while the NHTSA and the EPA plan to hold public hearings in Washington, Detroit and Los Angeles.

The Trump administration is arguing that increasing fuel efficiency requirements contributes to an increase in the cost of new cars and trucks, which generally have more advanced safety features than older vehicles. A new analysis, published jointly by the NHTSA and the EPA, says that freezing the target could save an estimated $2,340 on each new automobile and save $500 billion in “societal costs,” including reducing the number of highway fatalities.

Critics of the proposal are calling it a massive regulatory rollback and a “step backward” in the fight against climate change. The analysis released by the federal agencies acknowledges that freezing the standards would increase US fuel consumption by 2 to 3 percent, or roughly half a million barrels of oil per day. This, in turn, would lead to an increase in greenhouse-gas emissions.

The proposed policy changes also take aim at California’s unique ability to set its own fuel economy and emissions rules for the vehicles sold and operating in the state. Because of a federal waiver, California has been allowed to set emissions standards that are more stringent than federal law. California has long argued that this exception is necessary “due to California’s unique geography, weather and expanding number of people and vehicles,” according to the California Air Resources Board.

The proposed rules call for replacing California’s requirements with a less-stringent set of rules applying to all 50 states. The agencies say that this will help automakers hold down costs by allowing them to adhere to one set of standards. California Gov. Jerry Brown expressed anger at the proposal, saying in a statement, “California will fight this stupidity in every conceivable way possible.”