The Falls Church-based government contracting firm that performed a background investigation into Edward Snowden before he disclosed details of a secret federal surveillance program is under criminal investigation by the Office of Personnel Management, according to Sen. Claire McCaskill (D-Mo.).

McCaskill said Thursday at a Senate hearing that the investigation into USIS, whose original name was US Investigations Services, is based on the “systemic failure to adequately conduct investigations under its contract” with the federal government.

In a statement, USIS said it “has never been informed that it is under criminal investigation.” The company said it received a subpoena for records from OPM’s inspector general in January 2012 and fully cooperated with “the government’s civil investigative efforts.”

The company declined to confirm whether it had screened Snowden, saying the thousands of investigations it conducts for the government are confidential.

Snowden was working for another Virginia government contractor, Booz Allen Hamilton, when he disclosed details of National Security Agency surveillance of U.S. citizens. The case has thrown a spotlight on the government’s reliance on contractors for sensitive tasks. In 2011, more than 4.2 million government and contract workers had security clearances, and more than a third of them had top-secret access.

McCaskill spokesman Drew Pusateri said McCaskill was told of the investigation by OPM’s inspector general.

Patrick McFarland, the inspector general for OPM, told the committee that there are concerns about USIS’s background check into Snowden. “Yes, we do believe that there — there may be some problems,” McFarland said at the hearing, according to the Reuters news agency.

According to its Web site, privately held USIS has 100 contracts to provide background checks for more than 95 federal agencies. The company was established in July 1996 “as a result of the privatization of the investigative branch of the Office of Personnel Management,” according to the Web site.

The company’s has more than 6,700 employees, and its clients include the departments of Justice, State, Homeland Security and Defense, plus about a dozen intelligence agencies, including the NSA and the National Reconnaissance Office. USIS is part of Altegrity, which is in turn owned by Providence Equity Partners.