49 C.F.R. § 1503.621 – Amendment of pleadings.

(a) Filing and service. A party must file the amendment with the Enforcement Docket Clerk and must serve a copy of the amendment on the ALJ and all parties to the proceeding.
(b) Time. A party must file an amendment to a complaint or an answer within the following:
1. (1) Not later than 15 days before the scheduled date of a hearing, a party may amend a complaint or an answer without the consent of the ALJ.
2. (2) Less than 15 days before the scheduled date of a hearing, the ALJ may allow amendment of a complaint or an answer only for good cause shown in a motion to amend.
(c) Responses. The ALJ must allow a reasonable time, but not more than 20 days from the date of filing, for other parties to respond if an amendment to a complaint, answer, or other pleading has been filed with the ALJ.