The White House in mid-November announced a measure that requires a fuel efficiency equivalent of 54.5 miles per gallon for model year 2017-25 passenger cars and trucks.
The Environmental Protection Agency says the new standards would cut domestic oil consumption by 4 million barrels and avoid more than 2 billion tons of greenhouse gases over the lifetime of the model years outlined in the proposal.
But U.S. Rep. Darrell Issa, R-Calif., chairman of the House Oversight Committee called on automakers to reveal the details of negotiations with the White House.
"What did your company receive in return for its agreement not to challenge final standards?" he asked executives in a letter obtained by the Platts news service.
Issa suggested a federal bailout of Chrysler and General Motors was the impetus behind the agreement to raise fuel economy standards in the United States.
The National Automobile Dealers Association said it supports improvements in fuel economy but expressed concern the new standards would add $3,000 to the average cost of a vehicle and price most American consumers out of the market.