The Obama administration on Wednesday accused the largest private firm that conducts security-clearance background checks for the federal government of failing to perform quality-control reviews in its investigations of potential government workers.

The Justice Department has intervened in a civil lawsuit against Falls Church-based USIS, the company that conducted background checks of both former National Security Agency contractor Edward Snowden and government contractor Aaron Alexis, who shot and killed 12 people at the Washington Navy Yard.

The decision by the Justice Department marks an increase in the legal pressure on USIS, which is already under criminal investigation by the U.S. Attorney’s Office for the District.

The lawsuit alleges that USIS engaged in a practice known as “dumping.” Using its own software program, USIS released to the Office of Personnel Management background investigations that had not gone through the full review process , the lawsuit alleges.

USIS concealed its dumping practice and maximized its profits by improperly billing the government for investigations the firm knew were incomplete, according to the lawsuit. USIS, formerly known as United States Investigations Services, has been paid $334 million for its investigations this year.

“We will not tolerate shortcuts taken by companies that we have entrusted with vetting individuals to be given access to our country’s sensitive and secret information,” said Stuart F. Delery, assistant attorney general for the Justice Department’s Civil Division.

The lawsuit against USIS was filed in the U.S. District Court for the Middle District of Alabama by a former employee of USIS, Blake Percival, under the whistleblower provisions of the False Claims Act. According to Percival, USIS engaged in its dumping practice since 2008.

A spokesman for USIS said the company has been cooperating, “and will continue to cooperate, with the government’s investigation into these allegations.”

“The behavior by a small number of employees alleged in the complaint is completely inconsistent with our company values, culture and tradition of outstanding service to our government customers,” the USIS spokesman said. “USIS has taken these allegations seriously since they were first brought to our attention more than 18 months ago. . . . We have put in place new leadership, enhanced oversight procedures, and improved protocols that have been shared with OPM.”

No evidence has emerged that USIS cut corners when it vetted Snowden and Alexis. In the case of Alexis, an OPM official said last month that there are no red flags in the way his background investigation was conducted.

“OPM has reviewed the 2007 background investigation file for Aaron Alexis, and the agency believes that the file was complete and in compliance with all investigative standards,” said Merton W. Miller, OPM associate director for federal investigative services.

But the company has drawn the notice of lawmakers and the Justice Department. USIS is under criminal investigation over “broad issues,” including whether it misled officials about the thoroughness of its work, according to law enforcement officials. A number of former USIS employees have been charged with falsifying records.

A former USIS employee told The Washington Post recently that she felt under enormous pressure while working at the company and was concerned whether the work was adequate.

“I didn’t like the feeling, ‘Am I doing this right?’ ” said Ileana Privetera, who left her job at USIS in December after about five months. “I felt like we were doing something important.”

She said she was asked to finish as many as 10 cases in a day. Other employees said they worked long hours with little supervision reviewing confidential information at home, or sometimes at a table in a Starbucks coffee shop.

“It was like, wink wink, do this as fast as humanly possible,” said a former USIS investigator who spoke on the condition of anonymity to avoid crossing a former employer. “There was this intense pressure to do more and faster.”

A bipartisan group of senators is pushing for improvements in a background-check system they see as dangerously flawed.

“Given the systemic problems that recent high-profile events have uncovered, no one should be shocked by today’s announcement,” said Sen. Claire McCaskill (D-Mo.). “USIS’s contracting practices were a recipe for disaster and constituted a clear threat to our national security.”

McCaskill, along with Sen. Susan Collins (R-Maine), introduced legislation Wednesday to implement an automated review of public records and databases for any information that might affect a job applicant’s security clearance.

USIS, which has about 7,000 employees, last year processed nearly 2.3 million investigations and handles about 45 percent of all contracted background checks for OPM.

The 2006 contract at issue in the lawsuit required USIS to conduct the investigatory fieldwork on each prospective applicant.

“OPM does not tolerate fraud or falsification,” said Elaine Kaplan, acting director of OPM, which has contracted with USIS since 1996. “Bad actors are held accountable to the fullest extent of the law.”