The federal Hatch Act prohibits federal government employees from participating in political campaigns. The Act prohibits works at polls, holding a party office, assisting with campaign fundraising activities, etc. The National Association of Letter Carriers, six individual federal employees and certain local Democratic and Republican political committees (Ps) filed a complaint, asserting on behalf of themselves and all federal employees that 5 U.S.C. § 7324(a) (2) was unconstitutional on its face and seeking an injunction against its enforcement. A three-judge court was convened, and the case was tried on both stipulated evidence and oral testimony. The District Court then ruled that § 7324 (a) (2) was unconstitutional on its face and enjoined its enforcement. The court recognized the 'well-established governmental interest in restricting political activities by federal employees which [had been] asserted long before enactment of the Hatch Act,' 346 F. Supp., at 579, as well as the fact that the 'appropriateness of this governmental objective was recognized by the Supreme Court of the United States when it endorsed the objectives of the Hatch Act. United Public Workers v. Mitchell, 330 U.S. 75 (1947) ' Id., at 580. The District Court ruled, however, that United Public Workers v. Mitchell, 330 U.S. 75 (1947), left open the constitutionality of the statutory definition of 'political activity,' and proceeded to hold that definition to be both vague and overbroad, and therefore unconstitutional and unenforceable against the plaintiffs in any respect. The District Court also added, id., at 585, that even if the Supreme Court in Mitchell could be said to have upheld the definitional section in its entirety, later decisions had so eroded the holding that it could no longer be considered binding on the District Court. The Supreme Court granted certiorari.