49 CFR 821.9 - Intervention and amicus appearance.
(a) Intervention. Any person may move for leave to intervene in a proceeding, and may become a party thereto, if it is found that such person has a property, financial or other legitimate interest that will not be adequately represented by the existing parties, and that such intervention will not unduly broaden the issues or delay the proceeding. Except for good cause shown, no motion for leave to intervene will be entertained if filed less than 15 days prior to the hearing. The extent to which an intervenor may participate in the proceeding is wholly within the law judge's discretion.
(b) Amicus curiae briefs. A brief of amicus curiae in a matter on appeal from a law judge's initial decision or appealable order may be filed, if accompanied by written consent of all the parties, or by leave of the General Counsel if, in his or her opinion, the brief will not unduly broaden the matters at issue or prejudice any party to the proceeding. A brief may be conditionally filed with motion for leave. The motion for leave shall identify the interest of the movant and shall state the reasons why a brief of amicus curiae is desirable. Such brief and motion shall be filed within the briefing time allowed the party whose position the brief would support, unless good cause for late filing is shown, in which event the General Counsel may provide an opportunity for response in determining whether to accept the amicus brief.