5 U.S.C. § 552(b)(5) exempts “inter-agency or intra-agency memorandum or letters” which would be privileged in civil litigation.
Often invoked in cases of deliberative process involving agency lawyers, B5 can often broadly apply to material of public interest. Courts have determined that it correctly only applies to “pre-decisional” information, to protect free and frank debate about policy options.
Ryan v. Dept. of Justice, 617 F. 2d 781, 790-91 (D.C. Cir. 1980).