Federal investigators withheld information from Congress in a report on claims that Interior Department officials improperly pressured contractors for political reasons.

The pressure allegedly was to falsify data on job losses resulting from a proposed Interior Department Mining rule.

Assistant Inspector General for Investigations Robert Knox told the House Natural Resources Committee on Thursday that he feared his staff would lose access to important documents in the future if they disregarded an executive privilege claim by the Interior Department.

Executive branch officials must claim a defensible executive privilege before they can legally withhold documents sought by Congress.

"I also must again express my concern that Deputy Inspector General Mary Kendall is withholding information from Congress when the IG is charged with being an independent watchdog for Congress," said committee chairman Doc Hastings, a Washington state Republican.

"I have been vocal about the mismanagement of the IG’s office under the leadership of Ms. Kendall. As I’ve said before, we need a permanent IG," Hastings said.

Kendall, who has been in an acting capacity since 2009, also refused to provide emails and interview transcripts from her office's investigation, Hastings said.

Other members said the refusal to release the information was evidence of lack of transparency at the IG office.

"The role of the Office of the Inspector General, to me anyway, is about transparency, and transparency leads to — if not good government, better government — and so all of the all of the report redactions, I find that greatly troubling, given at least my perception of what OIG should be about," said Rep. Glenn Thompson, R-Pa.

Rep. Bradley Byrne, R-Ala., pressed Knox on the IG's choice to side with the department and withhold information because of the department's assertion of privilege.

"So you don't think it's the function of your office to, at least, ask for the waiver of the privilege so you can get to the point of having information that could potentially be important to rendering your judgement," Byrne asked.

"Actually, sir, I don't feel qualified to answer that question," Knox said. "I don't think we encounter this kind of stuff all that often, and it seems like we've had a couple of instances before this committee, but in my personal professional career, this is perhaps the first time I've dealt with it."

The IG report dealt with allegations that the Office of Surface Mining Reclamation and Enforcement pressured contractors working on an environmental review of proposed mining rules into changing job loss estimates for political reasons.

A major problem with the environmental review was OSM's poor management of the contractor conducting the review, Polu Kai Services, and its subcontractors, according to the unredacted portion of the IG report.

The redacted pages concern new problems with the Office of Surface Mining's unidentified current contractor, Knox said. He declined to comment on the redacted content.

Committee members said any new contract problems should be public because of OSM's problems with Polu Kai Services.

Thursday's exchange is only the latest example of the IG withholding information from the committee. Kendall ignored a 2012 subpoena for documents on the IG's investigation into a Gulf drilling moratorium report by Interior, according to Hastings.

He and other Republican members of the committee also rejected Knox's assertion that the IG investigation uncovered no evidence of political pressuring or undue influence by OSM over contractors.

"It is clear, based on the IG report and our findings, that the Obama administration wanted to hide the real job-loss numbers," Hastings said.

In a September 2012 report, Hastings' committee concluded that OSM did pressure contractors.

"It's pretty hard to come to a conclusion that where there's smoke, there's not some fire," Hastings said Thursday. "When you look at timeline, it's hard to say there may not be some interference in there."

A draft review by the contractor and two subcontractors projected that the proposed rule, which heavily revised a 2008 rule now under challenge in federal court, would wipe out 7,000 jobs to protect streams near mining sites.

After the job-loss numbers became public, OSM told the contractors to change their calculation of the job losses using the 2008 rule under legal challenge. They refused, arguing that using a hypothetical situation would result in incorrect estimates.

OSM officials claimed longstanding frustrations with the contractors, but didn't discuss firing them until after the leak, according to the IG report.

The agency ultimately decided to let the contract expire without renewal, according to the IG report.