Michigan's U.S. senators are backing a proposal that would allow automakers to apply credits for model years as far back as 2009 to help them meet future standards to require their car and truck fleets to average 41 miles per gallon by 2021, reports the Detroit News.

U.S. Senators Debbie Stabenow (D-Lansing) and Gary Peters (D-Bloomfield Township) have signed on as co-sponsors of the Fuel Economy Harmonization Act. They say the bill would address conflicts between NHTSA's Corporate Average Fuel Economy program and the EPA's Greenhouse Gas emissions programs.

Environmental groups have criticized the proposal as "another step in the automakers' push to roll back clean car and fuel economy standards," said Rhea Suh, president of the Natural Resources Defense Council.

President Donald Trump's administration is reviewing the mileage rules implemented by Obama's EPA that require an average of 50 mpg by 2025.