13 CFR § 134.210 - Intervention.
(b) By interested persons. Any interested person may move to intervene at any time until the close of record by filing and serving a motion to intervene containing a statement of the moving party's interest in the case and the necessity for intervention to protect such interest. An interested person is any individual, business entity, or governmental agency that has a direct stake in the outcome of the appeal. The Judge may grant leave to intervene upon such terms as he or she deems appropriate.
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