Focused on a large, diverse branch of the British postal workers’ trade union, workplace union responses to Royal Mail’s employee involvement initiatives are examined through a two-stage longitudinal case study. Royal Mail – the letters section of the British postal service – has carried out a series of managerialist experiments with employee involvement and participation in the last few decades, providing the basis for an important research literature on union and worker responses to new management initiatives, participation and HRM. Findings suggest that these management initiatives and union responses have mutated over time, with an ever-growing gap between management rhetoric associated with employee involvement and increasingly punitive management practice; and with changing but relatively resilient, oppositional workplace union responses. These developments are closely related to the entrenched, confrontational nature of Royal Mail industrial relations that has persisted since the mid-1980s.