The commission may require any public utility to file periodical reports, at such times, and in such form, and of such content, as the commission may prescribe, and special reports concerning any matter whatsoever about which the commission is authorized to inquire, or to keep itself informed, or which it is required to enforce. The commission may require any public utility to file with it a copy of any report filed by such public utility with any Federal department or regulatory body. All reports shall be under oath or affirmation when required by the commission.