5 U.S.C. § 7311: Loyalty and striking

An individual may not accept or hold a position in the Government of the United States or the government of the District of Columbia if he—(1) advocates the overthrow of our constitutional form of government; (2) is a member of an organization that he knows advocates the overthrow of our constitutional form of government; (3) participates in a strike, or asserts the right to strike, against the Government of the United States or the government of the District of Columbia; or (4) is a member of an organization of employees of the Government of the United States or of individuals employed by the government of the District of Columbia that he knows asserts the right to strike against the Government of the United States or the government of the District of Columbia.