The U.S. Department of Defense is falling behind on shrinking its civilian work force according to a report from the Government Accountability Office.

The 2013 National Defense Authorization Act passed by Congress mandated the department downsize. The mandate included cutting both active-duty military personnel and its civilian workforce at roughly the same rate. However, the GAO report shows troop levels are falling faster than civilian levels.

"The Department of Defense's (DOD) September 2014 and February 2015 reports did not fully address most statutory requirements identified in section 955 of the National Defense Authorization Act (NDAA) for fiscal year 2013," the report read. "DOD has made civilian personnel reductions; however, GAO's analysis indicates that the reductions may not achieve the savings required by section 955."

Section 955 of the National Defense Authorization Act 2013 requires the department to cut costs incurred by civilian and contractor work forces between fiscal years 2012 and 2017. According to the GAO report, full-time civilian positions declined by 3.3 percent, however civilian personnel costs declined by only 0.9 percent when adjusted for inflation.

"Because DOD's focus has been on making and reporting on FTE reductions, DOD and Congress lack information on the extent to which the reductions will achieve savings, and DOD may risk falling short of the statutory requirement for cost savings in the civilian workforce," the report continued.

Navy Times reports U.S. military leaders conceded that more work needs to be done to boost savings, however blame delays in accounting on differences in long-term budgets on Congressional mandates.

The Department of Defense employed approximately 22,000 full-time civilian workers in fiscal 2015, at a cost of almost $52 million.