Washington ( CNN ) -- The FBI said Friday it will respond to questions from Congress on the use of FBI aircraft amid allegations that Attorney General Eric Holder is among officials who `` may have used FBI planes for his own travel when aircraft were needed for FBI operations . '' Both the Justice Department and the Senate Judiciary Committee confirmed FBI Director Robert Mueller himself intends to reply to the allegations . A letter to Mueller from key congressional Republicans in the House and Senate said Thursday that in one case , Holder is alleged to have reserved an FBI aircraft , `` upgraded to a larger aircraft owned by a different agency and left the FBI plane sitting idle because he failed to notify the FBI in a timely manner . '' The letter from Sens . Chuck Grassley , R-Iowa , and Kay Bailey Hutchison , R-Texas , was also signed by powerful GOP House Judiciary Committee Chairman Lamar Smith of Texas and House Appropriations Committee Chairman Frank Wolf of Virginia . In May , Grassley asked Mueller , who was testifying on Capitol Hill , if the FBI had to lease a plane because the bureau 's jet was reserved for top Justice Department officials . Mueller responded : `` The Attorney General , the Department of Justice , the FBI , understand that these planes are first for investigative work , '' Mueller said . `` They are used for counterterrorism , criminal cases , and that any travel of the principals is secondary to the use of the plane for the investigative work of the FBI . '' The answer was not sufficient for Grassley and his colleagues . The lawmakers want to know why the FBI pays for Holder 's travel , even when he uses non-FBI planes such as Department of Defense or Federal Aviation Administration aircraft . Among several other demands , the lawmakers want the FBI to list all flights billed to the FBI by the Justice Department , and whether all of those flights were for official or personal travel . The letter , apparently coincidentally , was sent to Mueller on the day The Washington Post highlighted what it called `` Eric Holder 's world tour . '' The Post noted that Holder is planning a trip to the Middle East . He has already traveled this summer on official business to Denmark , Germany , Guam , Malaysia and Singapore . The article notes the attorney general appears to have itineraries packed full of official meetings , so he has little time for sightseeing . The expenses associated with the travel of attorneys general and other top government officials is an oft-debated topic in Washington . Frequently , the party out of power or its allies complain about the cost to taxpayers for official travel . Holder 's predecessor , Michael Mukasey , who served under President George W. Bush , was also questioned about his travel expenses . One of the major issues is the government 's requirement that for security reasons , attorneys general , Homeland Security secretaries , FBI directors , and many defense and civilian intelligence officials must fly in government aircraft . When these officials travel on personal business they must reimburse the government at the rate of a round trip coach fare . The cost of a round trip coach fare between Washington and New York , for example costs about $ 130 , while the actual cost of operating a government plane to and from New York to Washington is more than $ 4,000 . The taxpayers pay the difference .
Holder `` may have used FBI planes for his own travel when aircraft were needed for FBI operations '' FBI Director Robert Mueller will respond to the allegation by GOP leaders . Lawmakers want to know why FBI pays for Holder 's travel when he uses non-FBI aircraft .