As used in this subchapter, the phrase “unlawful employment practice” shall not be deemed to include any action or measure taken by an employer, labor organization, joint labor management committee, or employment agency with respect to an individual who is a member of the Communist Party of the United States or of any other organization required to register as a Communist-action or Communist-front organization by final order of the Subversive Activities Control Board pursuant to the Subversive Activities Control Act of 1950.