(a) Informal complaint. Any interested person desiring to complain of the lawfulness of any rate or charge made or proposed to be made for any stockyard service furnished at a stockyard by a stockyard owner or market agency, or rule, regulation or practice affecting any such rate or charge, may file an informal complaint with the Administrator.

(b) Investigation. If there appears to be any reasonable ground for doing so, the Administrator will investigate the matter complained of. If the Administrator reasonably believes that there are not sufficient facts to form the basis for further proceeding, the matter may be dropped. If it is dropped, the person filing the informal complaint will be informed.

(c) Status of person filing. A person filing an informal complaint will be a party to a rate proceeding if the Administrator files such person's informal complaint as a formal complaint, or if the Judge permits such person to intervene upon written application.

(d) Formal complaint. A rate proceeding may be instituted only upon filing of a formal complaint by the Administrator. A formal complaint may be filed on the initiative of the Administrator, or on the basis of an informal complaint, or by filing the informal complaint as a formal complaint. A formal complaint filed by the Administrator, or a summary thereof, will be published in the Federal Register, together with notice of the time by which, and the place where, any interested person may file a written request to be heard.