7 C.F.R. § 47.12
At any time after the institution of a proceeding and before it has been submitted to the Secretary for final consideration, the Secretary or the examiner as defined in § 47.2(i)(1) may, upon petition in writing and for good cause show, permit any person to intervene therein. The petition shall state with preciseness and particularity:
[10 FR 2209, Feb. 27, 1945, as amended at 60 FR 8459, Feb. 14, 1995; 64 FR 38107, July 15, 1999]