In December 2007, Congress approved an energy bill with a provision that prohibits federal agencies - the largest single buyer of fuel in the nation - from signing contracts to buy carbon-belching dirty fuels, such as those derived from tar sands. After its passage, the Department of Defense worked to revoke the law. In August, legislators stopped the department's attempt when they refused to attach an amendment that would repeal the law to the 2009 defense authorization bill. Members of Congress were guided in their decision by telephone calls and fact sheets from NRDC staff. Capitol Hill's action sends dirty fuel operators a clear message: the U.S. government is now expected to clean up its act.