Opinion of the Court
on public highways is directly at issue because the tax was an importation tax”). The incidence of a tax is a question of state law, Oklahoma Tax Comm’n v. Chickasaw Nation, 515 U. S. 450, 461 (1995), and this Court is bound by the Washington Supreme Court’s interpretation of Washington law, Johnson v. United States, 559 U. S. 133, 138 (2010). We decline the Department’s invitation to overstep the bounds of our authority and construe the tax to mean what the Washington Supreme Court has said it does not.
Nor would it make sense to construe the tax’s incidence differently. The Washington Supreme Court’s conclusion follows directly from its (and our) interpretation of how the tax operates. See supra, at 4–7. To be sure, it is generally true that fuel imported into the State by trucks driving the public highways can also be described as fuel that is possessed for the first time in the State. But to call the Washington statute a tax on “first possession” would give the law an over-inclusive label. As explained at length above, there are several ways in which a company could be a “first possessor” of fuel without incurring the tax. See ibid. For example, Cougar Den would not owe the tax had Cougar Den “first possessed” fuel by piping fuel from out of State into a Washington refinery. First possession is not taxed if the fuel is brought into the State by pipeline and bound for a refinery. §§82.36.026(3), 82.36.020(2)(c)(ii), 82.36.010(3). Similarly, Cougar Den would not owe the tax had Cougar Den “first possessed” fuel by bringing fuel into Washington through its waterways rather than its highways. First possession is not taxed if the fuel is brought into the State by vessel. §§82.36.026(3), 82.36.020(2)(c)(ii), 82.36.010(3). Thus, it seems rather clear that the tax cannot accurately be described as a tax on the first possession of fuel.
But even if the contrary were true, the tax would still have the practical effect of burdening the Yakamas’ travel.
