Some 83,000 Pentagon employees and contractors are tax deadbeats, to the collective tune of  $730 million. And, roughly a quarter of them had top-secret security clearance, an internal government audit shows.

It’s yet another reason the U.S. security clearance system is under scrutiny after high-profile former employees such as Edward Snowden started to reveal classified information. 

“Federal laws do not prohibit an individual with unpaid federal taxes from holding a security clearance, but delinquent tax debt poses a potential vulnerability,” the Government Accountability Office report says. “Because these clearances may allow personnel to access classified information that, through unauthorized disclosure, can in some cases cause exceptionally grave damage to the U.S. national security, investigators and adjudicators are to thoroughly assess applicants and their eligibility.”

The report cites IRS data showing roughly 40 percent of these workers had a repayment plan for their debt, and a quarter of them were eligible for a top-secret clearance level.

The U.S. security-clearance system has attracted a great deal of scrutiny thanks to Edward Snowden, the National Security Agency contractor who leaked thousands of secret documents, and most recently explained to the public how NSA workers treated sensitive photos and other information.

“Giving security clearances to individuals who fail to follow the law is unwise and risky,” Sen. Tom Coburn (R-Okla.) told The Hill Monday. “It is vital that the administration and Congress work diligently to eliminate potential threats that compromise the integrity of the federal workforce and the privileged information they safeguard,” he added.

As of October 2013 more than 5.1 million federal employees and contractors held or were eligible for a security clearance, the GAO said.