A Senate subcommittee is investigating allegations against a top federal auditor accused of nepotism, abuse of power and coverups.

Sens. Claire McCaskill (D-Mo.) and Ronald H. Johnson (R-Wis.), the chairman and ranking member of the homeland security financial and contracting oversight subcommittee, asked in a recent letter that Homeland Security Deputy Inspector General Charles Edwards cooperate with the panel’s probe.

The subcommittee is investigating nine claims against Edwards, including his alleged employment of his wife, Madhuri Edwards, as a supervisory auditor within his office, an apparent violation of laws and regulations governing personnel practices, the letter said.

When staff called attention to the matter, the auditor threatened retaliatory action, according to the letter, dated June 27.

Edwards also allegedly changed and withheld “relevant and damaging information” from an investigation into the Secret Service scandal involving prostitutes in Colombia. Former Secret Service director Mark Sullivan apologized last year for what he described as “misconduct” by his agents.

Whistleblowers have additionally accused Edwards of asking employees to do his schoolwork and write his dissertation for his doctorate. According to the letter, he also has been accused of using office funds to attend classes in Florida.

The senators have asked Edwards to provide documents and communications relating to the allegations by July 19.

“I am very disturbed that false allegations have been made against me, but more importantly, I am very concerned that this matter may negatively impact the important oversight work of the Office of Inspector General,” Edwards said in a statement Tuesday. “I will defend myself against these personal attacks.”

Edwards said that some of the allegations in the subcommittee’s letter had been reviewed and dismissed by other oversight bodies, including the Council of the Inspectors General on Integrity and Efficiency.

Edwards became acting inspector general for Homeland Security in February 2011, and he has served as deputy inspector general for the agency since January.