One of the Obama administration’s signature environmental proposals — requiring tough new fuel efficiency standards for cars — is under attack from a powerful lobby of car dealers. President Obama had forged an agreement with major U.S. automakers requiring that cars would get an average of 54 miles-per-gallon by 2025, nearly double current standards. After taking billions in government bailout money, carmakers like General Motors and Chrysler were under intense pressure to agree to the new standards, which are currently being formulated. But now thousands of U.S. automobile dealers are supporting Republican legislation that would upend that agreement and soften the fuel efficiency standards. The bill, introduced in the House of Representatives, would block the U.S. Environmental Protection Agency from being involved in fuel efficiency decisions, leaving the matter to the Department of Transportation. The car dealers say the agreement between Obama and the automakers bullies them and consumers into accepting overly strict mileage standards that will significantly increase car costs.