Administrative subpoenas are subject only to limited review. See, e.g., NLRB v. G.H.R. Energy Corp., 707 F.2d 110, 113 (5th Cir. 1982) (interpreting a statute granting subpoena power identical to that of the EEOC). Upon petitioning for enforcement of an administrative subpoena, the issuing agency must make a threshold showing that the subpoena is within the agency's authority, that the agency has satisfied statutory requirements of due process, and that the information' sought is relevant and material to the investigation.