Rutan v. Republican Party of Illinois
Rutan v. Republican Party of Illinois, 497 U.S. 62 (1990), was a United States Supreme Court decision that held that the First Amendment forbids a government entity from basing its decision to promote, transfer, recall, or hire low-level public employees based upon their party affiliation.
Source: Wikipedia — Rutan v. Republican Party of Illinois (CC BY-SA 4.0)