The attorney-client privilege provides such a fragile protection that disclosure to nearly any third party waives the protection. Does that general rule apply to communications among corporate affiliates? Surprisingly few decisions have addressed this issue.

In Cohen v. Trump, Civ. No. 13-CV-2519-GPC (WVG), 2015 U.S. Dist. LEXIS 74542 (S.D. Cal. June 9, 2015), the plaintiff claimed that a Trump entity waived its privilege by including in its communication an employee of another Trump entity. The court rejected plaintiff's waiver argument — confirming that "if a corporation with a legal interest in an attorney-client communication relays it to another related corporation, the attorney-client privilege is not thereby waived." Id. at *39. Interestingly, the court primarily relied on a 41-year-old District of South Carolina case. Duplan Corp. v. Deering Milliken, Inc., 397 F. Supp. 1146, 1184-85 (D.S.C. 1974). The most recent case cited by the court was nearly 20 years old. Id. at *39-40. One might have expected the court to rely on more recent case law.

Corporations should take comfort in this latest articulation of a principle that many lawyers think goes without saying.