50 C.F.R. § 37.43
If at any time while exploratory activities are being carried out under an approved exploration plan and special use permit, the Regional Director, on the basis of information available to him, determines that continuation of further activities under the plan or permit will significantly adversely affect the refuge's wildlife, its habitat, or the environment, or significantly restrict subsistence uses, or that the permittee has failed to comply with its approved exploration plan, plan of operation, special use permit, any reasonable stipulation, demand or order of the Regional Director, or any regulation of this part, the Regional Director may, without any expense or liability to the Department, suspend activities under the plan and/or permit for such time, or make such modifications to the plan and/or permit, or both suspend and so modify, as he determines necessary and appropriate. Such suspensions shall state the reasons therefore and be effective immediately upon receipt of the notice. Suspensions issued orally shall be followed by a written notice confirming the action within 3 days, and all written notices will be sent by messenger or registered mail, return receipt requested. A suspension shall remain in effect until the basis for the suspension has been corrected to the satisfaction of the Regional Director. For good cause, the Regional Director may also grant at the permittee's request, a written waiver of any provision of its special use permit, so long as such waiver will not be likely to result in significant adverse effects on the refuge's resources. Reconsideration of the Regional Director's actions under this section may be obtained by employing the procedures described in § 37.22(c) . A request for reconsideration shall not operate to stay the Regional Director's actions unless such stay is granted in writing by the Director.
50 C.F.R. §37.43