Federal decisions have recognized that injunctive relief against criminal investigations is available, but only under extraordinary circumstances where: (1) the constitutional violations are egregious; (2) there is an imminent threat of such future misconduct; (3) the threatened harm is irreparable; (4) there is no adequate remedy at law. See, e.g., Reporters Com. v. American Telephone & Telegraph, supra, 593 F.2d at p. 1065; Sullivan v. Murphy (D.C. Cir. 1973) 478 F.2d 938, 965 [156 App. D.C. 28]; Long v. District of Columbia (D.C. Cir. 1972) 469 F.2d 927, 932 [152 App. D.C. 187]; See also Note, the Federal Injunction as a Remedy for Unconstitutional Police Conduct (1968) 78 Yale L.J. 143. Triple a Machine Shop, Inc. v. State of California (1989) involved a combined civil and criminal proceeding initiated by the Attorney General and the San Francisco District Attorney for alleged unlawful disposal of hazardous wastes. The superior court granted a preliminary injunction prohibiting the district attorney from contacting present and former employees of the machine shop on the ground that such contacts violated the attorney-client privilege. The Court of Appeal reversed the judgment primarily on the basis of its findings that there was no violation of the attorney-client privilege or the work product privilege, but the court acknowledged the extent to which the doctrine of separation of powers influenced its decision. With respect to this issue, the court stated as follows: "The most significant effect of the injunction lies in its impact on the investigation and prosecution of the criminal charges. the separation of powers doctrine requires judicial restraint in enjoining criminal investigations or prosecutions. The prosecutor's authority stems from the executive branch of government (Cal. Const., art. III, 3), and the investigation and gathering of evidence relating to criminal offenses is the prosecutor's responsibility and rests solely within his or her discretion. (Hicks v. Board of Supervisors (1977) 69 Cal. App. 3d 228, 241 [138 Cal. Rptr. 101].) The discretionary authority vested in the district attorney to investigate and prosecute criminal conduct is considered too vital to the interest of public order to be subjected to prior restraint by the courts except under extraordinary circumstances. (Manchel v. County of Los Angeles (1966) 245 Cal. App. 2d 501, 505 [54 Cal. Rptr. 53]; Pitchess v. Superior Court (1969) 2 Cal. App. 3d 644, 648 [83 Cal. Rptr. 35]; Reporters Com. v. American Telephone & Telegraph (D.C. Cir. 1978) 593 F.2d 1030, 1065 [192 App.D.C. 376].) 'The balance between the Executive and Judicial branches would be profoundly upset if the Judiciary assumed superintendence over the law enforcement activities of the Executive branch upon nothing more than a vague fear or suspicion that its officers will be unfaithful to their oaths or unequal to their responsibility.' (Reporters Com. v. American Telephone & Telegraph, supra, at p. 1065.)" (Triple A. Machine Ship, Inc. v. State of California, supra, 213 Cal. App. 3d at pp. 144-145.)