49 CFR §605.31

On receipt of any complaint under § 605.30, or on the Administrator's own motion if at any time he or she shall have reason to believe that a violation may have occurred, the Administrator will provide written notification to the recipient (“Respondent”) that a violation has probably occurred. The Administrator will inform the respondent of the conduct which constitutes a probable violation of the agreement in a manner consistent with the fair notice requirements of 49 CFR 5.69.