43 C.F.R. § 4.1110 – Intervention.

(a) Any person, including a State, or OSM may petition for leave to intervene at any stage of a proceeding in OHA under the act.
(b) A petitioner for leave to intervene shall incorporate in the petition a statement setting forth the interest of the petitioner and, where required, a showing of why his interest is or may be adversely affected.
(c) The administrative law judge or the Board shall grant intervention where the petitioner—
1. (1) Had a statutory right to initiate the proceeding in which he wishes to intervene; or
2. (2) Has an interest which is or may be adversely affected by the outcome of the proceeding.
(d) If neither paragraph (c)(1) nor (c)(2) of this section apply, the administrative law judge or the Board shall consider the following in determining whether intervention is appropriate—
1. (1) The nature of the issues;
2. (2) The adequacy of representation of petitioner's interest which is provided by the existing parties to the proceeding;
3. (3) The ability of the petitioner to present relevant evidence and argument; and
4. (4) The effect of intervention on the agency's implementation of its statutory mandate.
(e) Any person, including a State, or OSM granted leave to intervene in a proceeding may participate in such proceeding as a full party or, if desired, in a capacity less than that of a full party. If an intervenor wishes to participate in a limited capacity, the extent and the terms of the participation shall be in the discretion of the administrative law judge or the Board.