A district court's review of an NLRB subpoena is "extremely limited," "extremely narrow," and of "a summary nature." NLRB v. G.H.R. Energy Corp., 707 F.2d 110, 113 (5th Cir. 1982); NLRB v. Frederick Cowan and Co., Inc., 522 F.2d 26, 28 (2d Cir. 1975). See also EEOC v. Bay Shipbuilding Corp., 668 F.2d 304, 310 (7th Cir. 1981); EEOC v. Suburban Transit System, Inc., 538 F. Supp. 530, 532 (N.D.Ill. 1982).