Republican congressman Darrel Issa (R-Calif.) threatened Tuesday to subpoena the nation’s foreign aid agency if it doesn’t hand over documents and information relating to alleged wrongdoing by top officials within the department.

Issa, who chairs the House Oversight and Government Reform Committee, demanded in a letter to U.S. Agency for International Aid Administrator Rajiv Shah that the department produce the documents by Monday evening.

The oversight committee is examining an inspector general’s investigation into possible contract rigging by the agency’s general counsel, as well as allegations that USAID’s second-ranking executive interfered with the probe.

The contract in question was for an adviser to USAID’s government-to-government direct assistance program, which is part of an agency initiative to improve the outcomes for foreign aid and wean developing nations off support.

An internal memo from the inspector general’s office indicates investigators were trying to determine whether USAID general counsel Lisa Gomer worked with former agency chief financial officer David Ostermeyer to create a six-figure contract that would go to Ostermeyer after he retired from the agency.

The document alleges USAID Deputy Administrator Donald Steinberg chastised investigators, telling them their efforts to gather information were “inappropriate” and that the case should have been taken to the front office before going to the Justice Department.

Issa has requested documents and communications relating to the contract and subsequent probes by the inspector general and the House oversight committee.

The congressman’s letter — co-signed by Rep. Jason Chaffetz (R-Utah), who chairs the oversight committee’s national security subcommittee — noted that corruption is prevalent in many developing nations that receive aid from the United States.

“It is therefore troubling that senior USAID officials … have themselves been implicated in allegations of contracting fraud and interference with an independent inspector general, whose job is to protect the taxpayer interest from this type of activity,” the letter said.

Corruption in prioritized countries and disaster areas is one of three “persistent problems” for USAID, according to the latest inspector general’s report on management challenges for the agency, from 2011.

Two-thirds of nations also scored in the lower half of the rating scale for Transparency International’s corruption perceptions index.

“Corruption amounts to a dirty tax, and the poor and most vulnerable are its primary victims,” the watchdog group said on its index Web site.

USAID said the State Department is reviewing the documents and communications Issa requested to determine whether any information is diplomatically sensitive.

“We will produce the responsive information to the committee after an interagency review of the documents is complete,” agency spokesman Kamyl Bazbaz said.

Bazbaz also said staff members from the House oversight committee have already reviewed some of the requested documents in person.