WASHINGTON, D.C. --- Michigan senators Carl Levin and Debbie Stabenow, along with five other senators, are pushing for a compromise that would relax pending fuel economy requirements spelled out in a Senate bill. In June, the Senate approved a 40-percent increase in fuel economy standards to 35 miles per gallon by 2020. This would apply to passenger cars, pickup trucks, SUVs and vans. In a letter to Senate leaders, Levin and Stabenow agreed that fuel efficiency standards should be bolstered, but they said the pending legislation "would have a needlessly detrimental effect on the auto industry and its workers." The group of legislators signing the letter favor several changes to the existing Senate plan, including a combined standard of 32 to 35 mpg by 2022 and separate standards for cars and trucks, the AP reported. Moreover, they favor provisions to maintain production of small cars in the U.S. and to extend credits for the building of flexible fuel vehicles through 2020. These credits are set to expire in 2010. The letter was signed by Levin, Stabenow, Mark Pryor of Arkansas, Russ Feingold of Wisconsin, Claire McCaskill of Missouri, Kit Bond of Missouri, and George Voinovich of Ohio. Last week, Allan Hubbard, director of President Bush's National Economic Council, sent a letter to House and Senate leaders saying that the council would recommend a veto of any energy bill that combined cars and trucks under the same fuel economy target, the Detroit Free Press reported. Hubbard also wrote that President Bush would receive a recommendation to veto the bill if it included tax increases or mandated renewable energy sources for electric utilities.