Public function doctrine is a legal principle that states that in a suit filed under 42 USCS § 1983 (Civil action for deprivation of rights), a private person's actions constitute state action if the private person performs functions that are traditionally reserved to the state.
The following are examples of case law discussing the doctrine:
The public-function doctrine requires that the private actor exercise "a power 'traditionally exclusively reserved to the State. [Edmonson v. Leesville Concrete Co., 500 U.S. 614, 640 (U.S. 1991)]
Under the "public function" doctrine, in the context of "under color of state law" for purposes of 42 U.S.C.S. § 1983, certain functions are regarded as the sole province of government, and ostensibly private parties performing such functions have been treated as state actors. The classic cases are the conduct of elections, and the governance of a "company" town. The public function test is based on historical practice, as opposed to a normative judgment. It is not enough that the function be one sometimes performed by government. Rather, where the party complained of is otherwise private, the function must be one exclusively reserved to the state. [Logiodice v. Trs. of Me. Cent. Inst., 296 F.3d 22 (1st Cir. Me. 2002)]