WASHINGTON (CNN) -- Federal agents on Tuesday raided the office of a federal whistle-blower protection agency and subpoenaed all 17 staffers, the FBI said.

The FBI seized computers belonging to agency chief Scott Bloch, sources say.

Law enforcement sources said agents seized computers belonging to Scott Bloch, the head of the Office of Special Counsel, an agency established in the 1970s to protect whistle-blowers and shield federal employees against improper management.

The sources said Bloch was the subject of a 2005 inquiry.

FBI spokesman Richard Kolko provided no details of the raids, which also involved agents from the inspector-general's office of the Office of Personnel Management.

James Mitchell, a spokesman of the Office of Special Counsel, said the agency was cooperating with investigators.

Bloch will remain on the job, and "nothing will change," he said.

"We do not yet know what this is about," he said. "Meanwhile, we are continuing to perform the independent mission of this office."

The U.S. attorney's office in Washington had no immediate comment on the investigation. But in December, the House Oversight and Government Reform committee asked Bloch to explain reports he hired an outside company to conduct a thorough erasure of files on a computer in his office and those of two top aides.

Bloch was already facing an investigation that began in 2005. A group that represents government whistle-blowers accused Bloch of obstructing justice, making false statements to Congress and retaliating against career employees he considered disloyal -- in one case, by attempting to transfer a dozen staffers to an office he sought to create in Detroit, Michigan.

"It is shocking that the individual who is primarily responsible for investigating federal whistleblower complaints would be the target of an investigation in which he and his staff are suspected of obstructing justice," Marshall Chriswell, a spokesman for the National Whistleblowers Center, said in a statement. The group called on the Bush administration to fire Bloch.

President Bush picked Bloch for a five-year term as the agency's director, a post he took in 2004, but the agency has been at odds with the White House during his tenure.

In 2007, Bloch's staff began investigating whether top Bush political adviser Karl Rove and other White House officials had used federal agencies for partisan political activities. And he also began looking into whether any laws were violated in the 2006 firings of U.S. attorneys in at least eight cities, which sparked House and Senate investigations as well.

Investigators from the Office of Personnel Management's inspector-general and the FBI already had begun looking into Bloch's activities. The Government Accountability Project, another group that supports government whistle-blowers, has accused Bloch of wading into the controversies in order "to keep himself in the public spotlight and protect against any efforts by the administration to hold him accountable."

Bloch is a former personnel lawyer who worked at the Justice Department's Faith-Based and Community Initiatives office before moving to the Office of Special Counsel.