MEMORANDUM *
We review the district court’s rejection of Plaintiff-Appellant Douglas Brown’s proposed jury instruction de novo because the rejection was based on a question of Idaho law. See Snake River Valley Elec. Ass’n v. PacifiCorp, 357 F.3d 1042, 1052 n. 11 (9th Cir.2004). The Idaho Supreme Court has not held that the causation standard for retaliatory discharge claims under the Idaho Protection of Public Employees Act, Idaho Code § 6-2101 et seq., is less stringent than the standard of “but for” causation. See Curlee v. Kootenai Cnty. Fire & Rescue, 148 Idaho 391, 224 P.3d 458 (2008). Moreover, while Jury Instruction 18 did require “but for” causation, it also stated that the protected activity “need not be the only cause” of the employment action. Because the district court’s jury instruction did not conflict with Idaho law, we AFFIRM.
We do not review Brown’s claim regarding the burden-shifting framework articulated in McDonnell Douglas Corp. v. Green, 411 U.S. 792, 93 S.Ct. 1817, 36 L.Ed.2d 668 (1973), because Brown has not proved he challenged this aspect of the jury instructions at the district court. See Bird v. Lewis & Clark College, 303 F.3d 1015, 1022 (9th Cir.2002).
AFFIRMED.