Third party labour contractors are increasingly prevalent in Global Production Networks (GPNs), and are a potential channel for ‘new forms of slavery’. Our review of case study evidence from South African and UK horticulture suggests unfree labour often emerges off-site through labour intermediaries. We examine analytical approaches to labour in GPNs and value chains. We argue that labour contracting is a logical extension of global outsourcing, helping to offset risk and enhance flexibility. A ‘cascade system’ allows unscrupulous intermediaries to exploit and coerce vulnerable workers. We examine strategies of civil society alliances, and regulatory reform, and argue for extending liability across global boundaries.