AbstractAlthough recent studies have demonstrated that union workers value job security, little research exists about what causes these perceptions and how unions might affect them. In this study, a job insecurity measure is developed and analysed using a sample of union members. The results indicate that the relationships between union variables and individual perceptions of insecurity depend on the organizational level at which threats occur (e.g. arbitrary supervision or organizational decline). Furthermore, for higher source‐level threats, union members are often sensitive to the wage‐employment trade‐off in that, if they perceive their union to effectively raise wages, they have higher levels of job insecurity. However, work rules do not appear to have much effect on reducing job insecurity percep