Pauline Hanson's chief-of-staff James Ashby is being investigated for allegedly flying a light aircraft without the correct licence.
The Civil Aviation Safety Authority inquiry reportedly centres on whether he was acting as a commercial pilot when he used a Jabiru J230 to fly his boss around Queensland during the 2016 federal election campaign.
If it is found Mr Ashby holds a recreational certificate or licence, but was operating as a commercial pilot, he could lose his registration.
Mr Ashby says the investigation is a "political witch-hunt".
"This matter has already been investigated by Recreational Aviation Australia where they found no case to answer," Mr Ashby said in a statement on Thursday.
"I will comply with CASA's request for documents, however, this is just a further waste of taxpayers' money where their findings will result in the same outcome as previous investigations."
A recreational certificate only allows pilots to fly a two-seat recreational registered aircraft in uncontrolled airspace during daylight hours within 25 nautical miles of the departed aerodrome.
A recreational pilot licence allows flights of larger aircraft in controlled airspace, and a private pilot licence is another step above that.
