First came the allegations that USIS, the company contracted to do many of the federal government’s background investigations, “flushed” 665,000 cases, creating what lawmakers said was a national security threat. Then came the revelation that the company also was put in charge of ensuring the quality of those investigations.

At a hearing earlier this month, lawmakers called that a flagrant conflict of interest. And Katherine Archuleta, the director of the Office of Personnel Management, moved quickly to change the policy, saying that now only the federal government — and not contractors — would do those quality reviews.

On Thursday, three Democratic senators, saying a new OPM director could reverse Archuleta’s order, introduced legislation that would prevent contractors from overseeing their own checks.

“Letting federal contractors review their own work is like letting the fox guard the henhouse,” said Jon Tester (D-Mont.), chairman of a subcommittee that oversees the federal workforce. Tester co-sponsored the bill with Sens. Claire McCaskill of Missouri and Mark Begich of Alaska.

The nation’s background security process has been in the spotlight ever since USIS acknowledged that it had conducted the background reviews for National Security Agency contractor Edward Snowden, who leaked thousands of classified documents that revealed many surveillance programs by U.S. intelligence agencies. The company also performed the background check on government contractor Aaron Alexis, who shot and killed 12 people at the Washington Navy Yard in September.

Last month, the Justice Department filed a complaint in a whistleblower’s lawsuit and alleged that USIS did not fully perform tens of thousands of background checks in an effort to meet performance incentives and reduce backlogs.

At a hearing earlier this month before the House Committee on Oversight and Government Reform, USIS chief executive Sterling Phillips reminded lawmakers that the company does not have the authority to grant security clearances, and that it only does the background investigations.

Since the allegations first surfaced, the company has appointed “a new leadership team, enhanced oversight procedures, and improved control protocols,” the company said in a statement.

Still, McCaskill said there needs to be more scrutiny of the process.

“It’s indefensible that contractors would ever have the authority to oversee themselves — particularly on work affecting our national security secrets and secure facilities,” she said. “It’s good news that the administration has taken swift action to strengthen accountability in the past several months, but we have to do more.”