The General Services Administration did not properly report hundreds of personal and other “nonmission” trips on government jets for senior Justice Department officials, including Attorney General Eric H. Holder Jr. and former FBI Director Robert Mueller, according to a watchdog report.

Congress’s nonpartisan Government Accountability Office determined that the 395 flights between 2009 and 2011 cost taxpayers $7.8 million. But a reporting exemption from the GSA, which oversees travel aboard federal jets, allows trips by intelligence officials to go undocumented, even in cases of unclassified personal travel.

The GSA regulation contradicts decades-old rules that President Bill Clinton and the Office of Management and Budget established, according to the report. The study said that the GSA “has not provided a basis for deviating from executive branch requirements.”

The GSA plans to eliminate the exemption that applies to non-mission, unclassified travel, according to the report. The agency also plans to document the trips in its periodic reports on travel by senior federal executives.

“Transparency remains a top priority for the agency,” said GSA spokeswoman Mafara Hobson. “That is why GSA is modifying its reporting tool to identify when agencies have classified flights.”

A 2013 GAO report revealed that the Justice Department spent $2.7 million on personal travel for Mueller and the attorneys general from 2007 through 2011, compared with about $8.7 million for business trips during that time.

Some senior federal officials are required for security reasons to use government aircraft when they fly, but they must generally reimburse the government at the rate of coach airfare for personal trips. The 2013 GAO report noted that the FBI director and attorneys general “provided reimbursements for their personal travel in accordance with federal requirements.”

Justice Department spokesman Brian Fallon said the agency makes travel information available to Congress and the public when they request the information under public records laws.

“If GSA intends to also report this information regarding unclassified, non-mission travel, we would have no objection at all,” Fallon said.

The report was released Thursday, nearly 19 months after Republican lawmakers began questioning Holder’s use of an FBI jet for travel unrelated to Justice Department work. Sen. Charles E. Grassley (Iowa), the ranking Republican on the Senate Judiciary Committee, had asked the GAO to look into the matter.

“There are legitimate reasons to keep some official travel classified, but non-mission travel by its own definition isn’t for national security or law enforcement purposes,” Grassley said Friday. “There’s no good reason for non-mission and personal travel to be hidden from the American taxpayers, who foot the bill for these flights.”

The FBI director was allowed to fly commercial until 2011, when the Justice Department required the chief to always use government aircraft to “access secure communication systems,” according to the 2013 report. Using federal planes can cost upward of $15,000 per trip, the GAO said.

The FBI reported personal air travel by its senior executives until 2009, when the agency realized that the GSA did not require documentation for trips by intelligence officials, according to last year’s GAO study.