WASHINGTON (Reuters) – The Sierra Club, Greenpeace USA and Public Citizen and other environmental and consumer advocacy groups plan to turn up the pressure on Wednesday in their campaign to stop automakers from lobbying the Trump administration to weaken fuel efficiency requirements.

The groups wrote last month to auto executives at Ford Motor Co, General Motors Co, Fiat Chrysler Automobiles NV, Toyota Motor Corp, Volkswagen AG (VOWG_p.DE) and others urging them to “discontinue any and all efforts to weaken or delay the implementation” of the 2025 fuel efficiency standards.

“The auto industry should be leaders in increasing efficiency and clean technology innovation, and now is not the time to go backwards. To do so would be dangerously misguided and have profound consequences,” they wrote.

The letters said the groups planned a national campaign to publicize the auto industry’s work with the Trump Administration to weaken fuel efficiency standards. The groups planned to kick off the effort Wednesday with a media event with U.S. Senator Sheldon Whitehouse dubbed “Forward, Not Backward: Stop the Rollback of Our Clean Car Standards.”

The Alliance of Automobile Manufacturers said it would not stop trying to convince U.S. regulators to lower fuel efficiency mandates approved in the final weeks of the Obama administration.

The carmakers said the costs would be onerous and the standards did not reflect how cheap gasoline was affecting consumer demand. They stopped short of asking for a specific reduction in requirements through 2025.

Automakers “are dedicated to continued gains in fuel efficiency and carbon reductions” the alliance said in a letter reviewed by Reuters, adding no one should “prejudge” the review’s outcome.

Ford wrote the environmental groups on Oct. 5 saying the company shares the goal “of reducing greenhouse gas emissions” but did not agree to any specific demands.

Automakers have urged changes that would make it easier for them to comply with fuel economy standards, including flexibility in the use of a system of credits under the program.

In June, New York state’s attorney general and 12 top law enforcement officials from other U.S. states said they would mount a court challenge if the administration tried to roll back vehicle emission rules.

The Obama administration finalized rules in 2012 to double the fleetwide average fuel economy to 54.5 mpg by 2025, but the EPA revised it to 51.4 mpg based on a rising number of trucks.