Officials with the U.S. Environmental Protection Agency say they will maintain fuel emissions standards set to take effect in about half a dozen years.
The move sets up a possible confrontation between the incoming and outgoing presidential administrations.
The EPA wants automakers to build cars that average about 50 miles a gallon and trucks that can reach about 40 miles a gallon by the year 2025.
Obama Administration officials were set to review the proposed requirement by April of next year.
But the head of the EPA says there has been almost a decade of research on the subject and the regulations should now be finalized.
The notice occurs about a week before the incoming Trump Administration takes office.
Auto industry executives say they hope the new President will take a second look at the regulations.
Automakers argue that meeting the standards will force them to pass the additional cost onto consumers.
Environmental groups counter that car companies have posted record sales in recent years despite already having to meet stricter emissions standards.