This article examines the collective, member-based Employers' Associations (EAs) in the UK that regulate the employment relationship by participating in collective bargaining. The main empirical contribution is to provide, for the first time, a longitudinal dataset of EAs in the UK.We use archival data from the UK Government's Certification Office to build a new dataset, identifying a decline of 81 per cent in the number of EAs between 1976 and 2013-2014. We also find that political agency and reducing levels of collective bargaining undermined EAs by reducing employers' incentives to associate, although changes within the UK's system of employment relations enabled other types of collective employer organisation to survive.