House lawmakers are examining whether a little-known department within the Environmental Protection Agency is blocking independent oversight efforts, as a federal investigator alleged in testimony he prepared for a hearing on Wednesday.

EPA Assistant Inspector General Patrick Sullivan said in remarks for the House Oversight and Government Reform Committee that the EPA’s Office of Homeland Security, run by the office of EPA Administrator Gina McCarthy, is acting as a “rogue law enforcement organization.”

EPA Administrator Gina McCarthy. (AP/Alex Brandon).

Sullivan said political appointees within the EPA have impeded efforts to determine whether the agency’s 10-person Homeland Security division has engaged in prohibited activities, including compelling employees to sign nondisclosure agreements while it was investigating employee misconduct, computer security and external threats.

EPA Deputy Administrator Bob Perciasepe said in prepared remarks for the hearing that the agency’s employees “work cooperatively to provide information to the Inspector General to ensure their important work is achieved.”

Perciasepe also said the EPA is committed to ensuring that the inspector general’s office is “successful in its efforts to root out waste, fraud, and abuse in every program office across the agency.”

The allegations against the Office of Homeland Security represent the latest development to cast doubt on the Obama administration’s ability to carry out effective oversight.

Homeland Security Secretary Jeh Johnson last month placed former Department of Homeland Security Inspector General Charles Edwards on administrative leave after a congressional investigation found that he had tailored reports to the liking of top DHS political appointees.

Probe: DHS watchdog cozy with officials, altered reports as he sought top job 

Separately, the Office of Special Counsel investigation found that senior officials working for the Commerce Department inspector general threatened subordinates with negative performance reviews if they did not sign gag agreements around the time the OSC was investigating the IG for possible wrongdoing.

The House subcommittee that oversees the department issued a letter last month calling on Commerce Department Inspector General Todd Zinser to fire two of his top managers over the findings. The probe found no evidence that Zinser was aware of the officials’ actions.

Questions also remain about why the Defense Department inspector general removed findings from a draft report that said former Defense Secretary Leon Panetta disclosed classified information about the Osama Bin Laden raid during a CIA awards speech attended by “Zero Dark Thirty” producer Mark Boal.

The final report, which the inspector general released in June 2013, did not include those details. It said the CIA took all appropriate measures to protect sensitive details from becoming public.

The House oversight committee plans to stream Wednesday’s hearing on the Office of Homeland Security live starting at 9:30 a.m.

Follow Josh Hicks on TwitterFacebook or Google+. Connect by e-mail at  josh.hicks(at)washpost.comVisit The Federal Eye, and The Fed Page for more federal news. Submit news tips and suggestions to federalworker@washpost.com.