Loyalty oath
A loyalty oath is an oath of loyalty to an organization, institution, or state of which an individual is a member.
In this context, a loyalty oath is not a pledge or oath of allegiance. It is an affirmation by which a person signs a legally binding document or warrant.
Usually, a loyalty oath to an organization or to a nation state is created during a time of social tension when people wish to guard against behavior like advocating fundamental change in the organization, advocating violent overthrow of the nation state, or spreading dissent within the organization. Such social tension is most manifest during times of war or when the organization or nation state is faced with a conflict with one or more other organizations or nation states (see Cold War).
On March 21, 1947, concerned with Soviet subversive penetration and infiltration into the United States government by American citizens who held oaths of allegiance to a foreign power during war time,
Democratic President Harry S Truman instituted a Loyalty Program, requiring loyalty oaths and background investigations on persons deemed suspect to holding party membership in organizations that advocated violent and anti-democratic programs.
http://en.wikipedia.org/wiki/Loyalty_oath