An inquiry into the competitive neutrality of the national broadcasters is set to commence shortly but the terms of reference, and the real purpose of the inquiry, remain a mystery.

According to Mitch Fifield's Department of Communications, the review -- first announced as part of the government's deal with One Nation senators to pass media ownership reforms last year -- will commence in the next couple of weeks and is expected to take around six months. It will be undertaken by an expert panel, but the terms of reference and format are still being finalised.