Abstract
This paper investigates the impact of industrial action at the workplace on union membership behaviour, in the form of joining (by non-members) and leaving (by members). It examines the issue from the perspective of exchange relationship theory. It is hypothesised that industrial action deepens the collective social and ideological aspects of exchange relationships and loosens the weaker individualist economic aspects, causing more workers to join than to leave a union. The data set comprises survey responses of random samples of individual workers continuously employed in the same workplace and collected at two points in time. Logistic regression is employed to analyse the data. The results demonstrate that workplace industrial action is associated with union joining but has no significant effect on members' leaving behaviour. Implications for union organising are discussed.