14 C.F.R. § 305.1
The provisions of this part shall govern informal nonpublic investigations, as distinguished from formal investigations and adjudicatory proceedings, undertaken by the Office of the Assistant General Counsel for Aviation Enforcement and Proceedings with a view to obtaining information from any person. While the Department seeks and encourages voluntary cooperation and believes that it is in the best interest of all parties concerned, it will utilize the procedures provided by this part to compel the disclosure of information by any person where DOT wishes to determine whether such person, or any other person, has been or is violating any provisions of 49 U.S.C. Subtitle VII, Chapter 411 or 49 U.S.C. 40102(2) , 41502 , 41507 , 41508 , 41509 , 41702 , 41703 , or 46101 , or any rule, regulation, order, certificate, permit, or letter or registration issued pursuant thereto by DOT and when the information appears to be relevant to the matter under investigation. This part shall not apply to employees or records of other agencies of the U.S. Government, the District of Columbia, or the several States and their political subdivisions.
14 C.F.R. §305.1