49 CFR § 1130.1 - When no damages sought.
(a) Form and content. Informal complaint may be by letter or other writing filed with the Board and will be serially numbered as filed. The complaint must contain the essential elements of a formal complaint as specified at 49 CFR 1111.2 and may embrace supporting papers.
(b) Correspondence handling. When an informal complaint appears susceptible of informal adjustment, the Board will send a copy or statement of the complaint to each subject of the complaint in an attempt to have it satisfied by correspondence, thereby avoiding the filing of a formal complaint.
(c) Discontinuance of informal proceeding. The filing of an informal complaint does not preclude complainant from filing a formal complaint. If a formal complaint is filed, the informal proceeding will be discontinued.