There is an extensive literature on supply chain collaboration but scant attention has been given to the management of human resources within buyer-supplier relationships. Two case studies of highly interdependent supply relationships were conducted: one an inter-organisational and the other an intra-organisational environment. A total of 84 semi-structured interviews were held with a wide cross-section of employees and managers at multiple levels across the two dyads. Findings highlight the pervasive effects of HR practices and the similarities of inter- and intra-firm contexts, which point to common HR characteristics within supply relationships. Institutional theory was used as a theoretical lens to throw light on the cognitive, normative and regulative mechanisms that underpin the management of HR practices within supply relationships. This research takes a cross-disciplinary approach to highlight the role of HR practices as integration mechanisms in the supply chain.