Third party call centres are growing as employers respond to market pressures. However, evidence shows their employees' experience of work is inferior compared to those working for in-house call centres. Drawing on research in two organizations we argue that the differences in employees' experiences can be explained by examining external influences on HR practices. These cases reveal a complex web of relationships involving clients, owners and Temporary Work Agencies. The strategic choice of HR practices is severely constrained by these important external parties and by the labour market making it difficult to develop effective, stable, mutually beneficial employment relationships. The impact of these external influences has implications for employee representation and legal protection in third-party call centres and for future research into the constraints on HR decision-making in these organizations.