Attorney General Eric Holder has required the Department of Justice's official watchdog to get permission for sensitive documents in several recent investigations, which hinders the investigator's independence, delays reports and raises legal snags, Inspector General Michael Horowitz told a Senate panel.

During the DOJ IG's investigations of Fast and Furious and the Foreign Intelligence Surveillance Act, the department required Horowitz to go through Holder to get crucial information on wiretaps and a grand jury report.

That only changed when Holder decided the reviews "were of assistance to them," Horowitz told the Senate's Subcommittee on the Efficiency and Effectiveness of Federal Programs and the Federal Workforce during a Nov. 19 hearing.

"While the Attorney General and Deputy Attorney General have made it clear that they will continue to provide the OIG with the necessary authorizations to enable us to obtain records in future reviews, requiring an inspector general to obtain a memorandum from department leadership in order to be allowed to review critical documents in the department’s possession impairs our independence and conflicts with the core principles of the Inspector General Act," he said.

Horowitz said his staff encountered similar delays in gaining access to FISA data.

Being required to obtain permission for important information from the very agency it's investigating handicaps an IG's independence and ability to properly do its job, Horowitz said.

In FISA cases, DOJ officials also determine which documents are relevant to an investigation.

The IG Act gives the federal government's internal investigators prompt access to any document they deem relevant to an investigation, according to the panel's witnesses.

"Although our office has not yet had an instance where materials were ultimately withheld from us that were necessary to complete our review, we remain concerned about the legal questions that have been raised and the potential impact of these issues on our future reviews," Horowitz said.

Other IGs have also experienced delays and interference with their independence by agency executives.

"Our principal challenges pertain to independence concerns and to timely access to information," said Peggy Gustafson, Small Business Administration IG, who also represented the Council of Inspectors General on Integrity and Efficiency at the hearing.

Her office frequently must negotiate with SBA for access to documents the agency claims are protected and shouldn't be disclosed, a spokesman told the Washington Examiner. It's not a new issue, but each audit can bring with it new problems and delays.

Such discussions can stall an investigation for months, the spokesman said. But the IG is part of the agency, and the IG Act entitles investigators access to the documents they need whether or not the agency thinks they're relevant, the spokesman said.

An agency might claim attorney-client privilege, for instance, and argue the documents shouldn't leave the agency.

The Environmental Protection Agency IG encountered delays in an August investigation when the U.S. Chemical Safety and Hazard Investigations Board withheld documents on the basis of attorney-client privilege, according to a September letter from the EPA IG.

IGs also fight what Horowitz called "over-classification" of information, and negotiate with agency officials for the public release of information in finished reports.

"We end up pushing back very strongly, and having a, in many instances, I’ll call it a robust discussion, internally," he told the Senate panel.

"We ultimately don’t control the final decision, it is not our information, but we do push forward very aggressively in ensuring that when we think there’s an over-classification in response to our report, we fight internally and often elevate it within the department and frequently prevail, frankly," he said.

Washington Examiner intern Ethan Barton contributed to this report.