Generally, an administrative subpoena is enforced through the courts.  An administrative agency must request a district court to enforce its subpoenas.  An order issued by a district court that enforces an administrative subpoena is a final order that can be appealed as a matter of right[i].

Even if the district court retains jurisdiction to grant further relief, the finality of the order is not defeated[ii].  An order by a magistrate judge in a subpoena enforcement proceeding is generally not considered as a final one until it is reviewed by a district judge[iii].

However, an appeal from a district court order enforcing an administrative subpoena becomes moot once the party has complied with the subpoena.  When the party has complied with the subpoena and the other party issuing the subpoena has obtained the testimony or documents it is seeking, then there is no longer a live controversy between the parties[iv].

[i] United States v. McDonald, 313 F.2d 832 (2d Cir. N.Y. 1963)

[ii] Cusumano v. Microsoft Corp., 162 F.3d 708 (1st Cir. Mass. 1998)

[iii] Strong v. United States, 57 F. Supp. 2d 908 (N.D. Cal. 1999)

[iv] NLRB v. Bacchi, 2004 U.S. Dist. LEXIS 20763 (E.D.N.Y. May 19, 2004)