Many environmentalists are pleading with President Donald Trump not to roll back fuel economy rules for vehicles put in place by President Obama.

Automakers have been vocal in their support for more relaxed mpg rules but during a recent public comment hearing organize by the U.S. Environmental Protection Agency (EPA), many voiced their concerns about potential changes.

“I’m here today to call on EPA to continue the tremendous success and leadership of its clean cars program, and to condemn the current administration’s signals that it will recklessly weaken these standards and shortchange EPA’s role,” said senior attorney for the Environmental Defense Fund’s U.S. Climate Legal and Regulatory program, Martha Roberts.

Under the previous administration, President Obama enacted stringent EPA rules between the 2017 and 2021 model years and then between 2022 and 2025. Under the current rules, carmakers need to achieve a fleetwide average of at least 35 mpg for 2017, 36 mpg for 2018, 37 mpg for 2019 and 39 mpg in 2020. Rules were then to become tighter until they reached 54.5 mpg in 2025.

The Detroit News reports that the Alliance of Automobile Manufacturers is a key supporter of the administration’s plan to loosen these rules.

In a statement, the lobby group’s vice president of energy and environment, Chris Nevers said “to keep costs reasonable for buyers and maximize future production levels and fleet turnover, it is vital to clearly focus on consumer preferences and market realities.”

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