This study examines the nature of collective action (unionisation) in the manufacturing sector in Singapore, using the social psychological analytical framework as proposed by Guest and Dewe (1988). It was found that among the four explanations of union joining, influence from colleagues emerged as the most important discriminator between members and non-members. This was followed by the costs and benefits of joining a union. Employee dissatisfaction as well as personal and job characteristics did contribute to the prediction of membership status but were of lesser significance. Implications of the findings highlighted the need to further our understanding of how group dynamics affect the unionisation process and how current recruitment strategies can be improved. With a sound appreciation of the demand for and supply of union services in Singapore, this will bring present membership growth to even newer heights.