Car companies that have pushed the administration for relief on stringent emissions and mileage requirements are also urging consistency around the country.
President Trump has vowed to review the federal vehicle emissions standards for 2025 to ensure that they are not hurting manufacturing jobs, reversing an Obama-era decision.
California and the 12 states that have signed onto its rules have fought the move, deciding last month to plow ahead with their 2025 standards and to start drafting goals for 2030.
The looming showdown could mean uncertainty for the auto industry, which has already invested in technologies to reach the 2025 targets and global efficiency standards.
"The notion that mutually assured destruction where California walks and creates a challenge, or the feds create a challenge on their part, neither of those is a good outcome," said Mitch Bainwol, president of the Alliance of Automobile Manufacturers, at a New York International Auto Show event yesterday.
"What we need at the end of the day is predictability, we need certainty, we need stability in regulation," he said. "It needs to be rational."
Bainwol said the White House had signaled to him that it would invite California, the federal Transportation Department, U.S. EPA and other federal partners to broker an agreement for one uniform system.
Bainwol had urged Gary Cohn, director of the National Economic Council, to start the process "as soon as possible" in a letter shortly after Trump announced he would reconsider whether to loosen the requirements.
The White House and automakers have denied they are seeking a rollback of the rules, but environmental advocates fear any changes could mean more pollution and fuel use.
"The talk of a rollback is fallacious," Bainwol said. "What we're talking about here is the nature of the slope. We will get to the Obama numbers; we will get beyond the Obama numbers. The question is, when?"
John Bozzella, president of the group Global Automakers, said the commitment to increasing fuel efficiency is "bedrock solid" but that automakers are already facing a "crazy patchwork" of regulations.
EPA, the National Highway Traffic Safety Administration and California set the rules in parallel under an agreement brokered by the Obama administration.
"We all committed back in 2011 to try and get that done, to get the regulatory drag out of the system and see if we can get one clear system," Bozzella said.
EPA and NHTSA have until April 2018 to decide whether to loosen the requirements.