37 CFR §42.9

1. (a)Entire interest. An owner of the entire interest in an involved application or patent may act to the exclusion of the inventor (see § 3.71 of this title).
2. (b)Part interest. An owner of a part interest in the subject patent may move to act to the exclusion of an inventor or a co-owner. The motion must show the inability or refusal of an inventor or co-owner to prosecute the proceeding or other cause why it is in the interests of justice to permit the owner of a part interest to act in the trial. In granting the motion, the Board may set conditions on the actions of the parties.