Jilin Pharm. USA, Inc. v. Chertoff, 447 F.3d 196 (3d Cir. May 10, 2006) (decision by the attorney general under 8 U.S.C. 1155 to revoke a prior approval of a visa petition was an act of administrative discretion that was statutorily shielded from court review, even as to constitutional claims).
http://caselaw.lp.findlaw.com/data2/circs/3rd/052788p.pdf