*2 The complaint asserts federal claims based on the Securities Exchange Act of 1934 (the “Exchange Act”) and Rule 10-b-5 promulgated thereunder, 15 U.S.C. § 78j(b); 17 C.F.R. § 240.10b-5, as well as common law claims of negligence and fraud based on diversity and supplemental jurisdiction. While Rule 501 of the Federal Rules of Evidence requires the application of federal privilege law to federal question claims and state privilege law to state law claims, Bondi v. Grant Thornton Int'l, 04 Civ. 9971(LAK), 2006 WL 1817313 at *2 (S.D.N.Y. June 30, 2006), citing
Bank Brussels Lambert v. Credit Lyonnais (Suisse) S.A., 160 F.R.D. 437, 441 (S.D.N.Y.1995) and
G-I Holdings, Inc. v. Baron & Budd, 01 Civ. 0216(RWS), 2005 WL 1653623 (S.D.N.Y. July 13, 2005), the Federal Rules of Evidence do not specify which law is to be applied where a proceeding includes claims based on both federal and state law. See
Jaffee v. Redmond, 518 U.S. 1, 15 n.15 (1996) (noting “disagreement concerning the proper rule in cases [where] relevant evidence would be privileged under state law but not under federal law”); 3 Jack B. Weinstein & Margaret A. Berger, Weinstein's Federal Evidence
§ 501.02[c] (Joseph M. McLaughlin ed., 2d ed. 2006) (“Rule 501 is not clear on which rule should be followed” where state and federal law claims are raised in same action). Nonetheless, the law is clear in this Circuit that federal privilege law should be applied to evidence relevant to both federal and state law claims. See
von Bulow v. von Bulow, 811 F.2d 136, 141 (2d Cir.1987); Bayne v. Provost, 359 F.Supp.2d 234, 238-39 (N.D.N.Y.2005); Boss Mmg. Co. v. Hugo Boss AG, 97 Civ. 8495(SHS)(MHD), 1999 WL 47324 at *1 (S.D.N.Y. Feb. 1, 1999). Here, because the 4-25-03 E-Mail is relevant to both plaintiff's federal and common law claims, I conclude that the present motion is governed by principles of federal law.