Purpose – The purpose of this paper is to test the ability of the theory of planned behaviour to predict worker intent towards an employee involvement (EI) programme, and the impact of union identification on workers’ decision making. Design/methodology/approach – Union workers at a small manufacturing company in the Midwestern United States completed two questionnaires. The first questionnaire provided measures of the attitudinal, normative, and behavioural control components of the theory of planned behaviour and the degree to which they identified with their labour union. In the second questionnaire, the same respondents answered questions to measure their intention to support or oppose an employee involvement (EI) programme. Findings – Intentions to support EI were accurately predicted from attitudes, normative support, and perceived behavioural control (0.05 level). Level of union identification moderated the impact of attitudes on intention to support EI for workers that did not identify heavily with the labour union (0.05 level), but did not moderate the effect of normative support on intention for workers who identified heavily with the labour union. Research limitations/implications – The results indicate that the theory of planned behaviour has the potential to be an effective tool in predicting the behavioural outcomes of union members in the workplace, and that the level of union identification affects decision making. Research is limited by same source methodology and no direct measure of behaviour. Practical implications – Leaders, labour and management, who intend to implement new programmes, should give strong consideration to how workers’ social cohorts influence their decision making and plan for this contingency when considering programme changes. Originality/value – The level of union identification influences perception and decision making but has not been considered in models of member decision making. EI research has tended to center on EI as the antecedent to outcomes such as job satisfaction, cooperation, retention, and quality of work life. This paper addresses the role of union identification in support for EI programmes, and uses a well-established behavioural theory to explain workers’ decision-making process.