term:

Scab

scab n

1 : a worker who refuses to join a labor union
2 : a union member who refuses to strike or returns to work before a strike has ended
3 : a worker who accepts employment or replaces a union worker during a strike
: strike breaker
4 : one who works for less than union wages or on nonunion terms

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.