In Bivens v. Six Unknown Federal Narcotics Agents, 403 U.S. 388, 91 S.Ct. 1999, 29 L.Ed.2d 619 (1971), the Supreme Court authorized a suit for damages against federal officials whose actions violated an individual's constitutional rights, even though Congress had not expressly authorized such suits. However, the Court added, this remedy is not available when "special factors counselling hesitation" are present. Id. at 396, 91 S.Ct. at 2005.