49 CFR §605.30

Any interested party may file a complaint with the Administrator alleging a violation of 49 U.S.C. 5323(f) or the terms of an agreement under § 605.14 (“Complaint”). A complaint must be in writing, must specify in detail the action claimed to violate the agreement, and must be accompanied by sufficient evidence to enable the Administrator to make a preliminary determination as to whether there is probable cause that a violation has taken place.