A union buster is an individual or organization that works to prevent the formation of labor unions or to weaken existing unions. ANNULMENT is the legal process of canceling a contract or agreement, and SCAB is a derogatory term for someone who takes the place of a striking worker. Seceder is someone who withdraws from an organization or alliance. Together, these terms describe someone who works to prevent the formation of labor unions or to weaken existing unions by taking the place of striking workers and withdrawing from organizations or alliances.