When parties with a common interest share attorney work product with each other in anticipation of litigation, the parties often expect that the work product will be immune from disclosure in the subsequent litigation. If, however, a party shares work product with another party with whom it has a common interest but also is a potential adversary, the work product may be discoverable by third parties, notwithstanding that the sharing parties had a common interest at the time they exchanged the work product.

U.S. Magistrate Judge Gabriel W. Gorenstein for the Southern District of New York recently addressed this exact issue in Pilkington N. Am. v. Mitsui Sumitomo Ins. Co. of Am., 341 F.R.D. 10, 16 (S.D.N.Y. 2022). Prior to the litigation, the eventual plaintiff, Pilkington North America, exchanged attorney work product with its insurance broker, Aon Risk Services Central, with which it shared a common interest at the time, but which it later named as a defendant in the action. Notwithstanding the common interest, Judge Gorenstein held that the work product was discoverable by the other defendant in the action, Mitsui Sumitomo Insurance Company of America (MSI), because (1) when the documents were exchanged, Aon and Pilkington were foreseeable adversaries and (2) the work product concerned the subject matter of the potential dispute between the parties. The ruling bespeaks caution to parties considering sharing work product with a party who may later become an adversary.

‘Pilkington v. MSI & Aon’