14 C.F.R. § 13.206 – Intervention.

(a) A person may submit a motion for leave to intervene as a party in a civil penalty action. Except for good cause shown, a motion for leave to intervene must be submitted not later than 10 days before the hearing.
(b) The administrative law judge may grant a motion for leave to intervene if the administrative law judge finds that intervention will not unduly broaden the issues or delay the proceedings and—
1. (1) The person seeking to intervene will be bound by any order or decision entered in the action; or
2. (2) The person seeking to intervene has a property, financial, or other legitimate interest that may not be addressed adequately by the parties.
(c) The administrative law judge may determine the extent to which an intervenor may participate in the proceedings.