In this article we analyse the reasons for active trade union participation within the context of Spanish industrial relations. Spain represents a particularly interesting case as the unions' main activity, collective bargaining, is considered a public good. The present study is based on a representative survey of one region of the 'Worker Commissions' trade union and provides empirical evidence that union presence in the workplace has a significant influence on members' propensity for activism. Union presence in the workplace enhances collectivism and builds incentive for action in inclusive systems of industrial relations. By contrast, individualistic orientations and instrumental motives are of little relevance in the Spanish industrial relations context. © Blackwell Publishing Ltd/London School of Economics 2010.