One of the key factors in the success of labour federations is to have affiliate unions who actively participate and support their work. This article examines the catalysts behind union involvement with central labour bodies and presents an analysis of the organizational motivations for engagement. The article uses comparative case study analysis to examine affiliate union commitment in the United States to the American Federation of Labor–Congress of Industrial Organizations' state federations, area labour federations and central labour councils. Union leadership, along with contextual, interpretative and organizational factors, was found to influence the level of affiliate union involvement in central labour bodies.