To conceptualise the labour supply chain and its relationship with product supply chains. In doing so, we call for research that follows the flow of labour to advance the field of Operations and Supply Chain Management (OSCM) towards decent work in supply chains. A real-time case study of modern slavery in the wine, apple and poultry supply chains in Southern Brazil with interviews including workers, farmers, and a multitude of stakeholders. By following the flow of labour, we uncover how temporary workers are used to manage product seasonality, and the role of hidden actors such as labour providers and charities. We show that different product supply chains tend to mimic each other and share the same pool of temporary workers to ensure flexibility at low cost, while exploiting workers. For decades the OSCM field has used frameworks that follow the product to improve efficiency and traceability. Yet, labour flows across product supply chains remain untraceable. Our research calls for a dynamic perspective on labour to set the basis for an emerging research agenda on the interplay of product and labour flows in supply chains to advance decent work.