Sen. Claire McCaskill, D-Mo., has long been critical of the way the government contracts out counternarcotics work, saying it has been “monopolized by large contractors” without sufficient competition (J. Scott Applewhite/AP)

Sen. Claire McCaskill (D-Mo.) called Tuesday for a review of counternarcotics contracts, after a Pentagon investigation found that Northrop Grumman and one of its subcontractors improperly charged the U.S. government more than $100 million in “questionable” costs.

The report by the Defense Department’s inspector general found $21.7 million in “potentially excessive payments” for overtime from October 2007 to March 2013 by Falls Church-based Northrop and DynCorp. The problems included one employee who billed $176,900 for 1,208 hours in a 12-day period — or more than 100 hours a day.

The inspector general also found that DynCorp, a subcontractor, had 360 employees working on the contract who did not meet the specified labor requirements, leading to $91.4 million in questionable costs.

In one case, a program manager who billed 5,729 hours over a year and a half, totaling $1.2 million, did not have a bachelor’s degree, which was a requirement of the position. Another employee billed 16,270 hours worth $2 million over five years but was qualified for only 161 hours of the work.

Pentagon investigators said that $10 million was spent on 33 employees who may not have been qualified. DynCorp told the inspector general that it couldn’t determine the employees’ qualifications “because some personnel files were archived and extremely difficult to obtain.”

The inspector general criticized the Army contracting agency for not verifying the labor requirements and invoices. The investigation began after a whistleblower called the inspector general’s hotline to report the improper billing.

The two companies were hired to supply spare parts, maintenance and training for the Afghan Defense Ministry, the Afghan Army Air Corps and the Afghanistan Interior Ministry’s Counter-Narcotics Air Squadron.

Northrop has said it has been cooperating with the inspector general. DynCorp has maintained that it complied with the contract and did nothing wrong. The Army said it is working to recoup the money.

McCaskill, the chairman of the Senate Homeland Security and Governmental Affairs subcommittee on financial and contracting oversight, called for the Pentagon “to explain how the overbilling occurred and how the DOD plans to recover the improper charges,” her office said in a statement.

She also called for the State Department ’s inspector general to “ensure that similar overbilling has not occurred under the State Department’s current counternarcotics contracts.”

McCaskill has long been critical of the way the government contracts out counternarcotics work, saying it has been “monopolized by large contractors” without sufficient competition. She also has accused government agencies of insufficient oversight and a lack of transparency.