A US rule that would require automakers to double fuel economy of cars and light trucks by 2025 was written "in secret, outside the scope of law," Representative Darrell Eisa said in a letter announcing a congressional investigation.
Eisa, a California Republican who is chairman of the House Oversight and Government Reform Committee, said in a letter to the US Transportation Secretary Ray LaHood that the rule was rushed and may jeopardise safety by forcing automakers to make lighter-weight vehicles.
"I am concerned about the negative impact these standards could have on the safety of automobiles, the possibility that the National Highway Traffic Safety Administration acted outside the scope of congressionally delegated authority and the lack of transparency in the process leading up to the agreement," Eisa said in the letter.
The agency oversees both fuel economy and safety regulation.
Eisa's panel announced investigations into the auto regulator and the Environmental Protection Agency, which wrote the rule along with NHTSA. "Safety considerations were central to establishing a national programme to improve fuel economy and reduce greenhouse gas emissions for passenger cars and light trucks through model year 2016," Olivia Alair, a Transportation Department spokeswoman, said in an e-mail.
"Likewise, safety continues to be our top priority as we move toward a proposal for standards for model year 2017-2025 vehicles."
Eisa also questioned the EPA's role in writing a previous fuel-economy rule that takes effect next year, saying it negotiated with automakers around the same time General Motors and Chrysler were getting US bailout money.
The timing "heightens the concern that the administration used the promise of taxpayer dollars to obtain GM and Chrysler's support for the new fuel economy standards" in 2009, Eisa said in a letter to EPA Administrator Lisa Jackson.
"EPA will respond as appropriate and we will continue to work with all our partners to continue to move forward on this historic clean-cars initiative," Alcantara Betsaida, an EPA spokeswoman, said in an e-mail.