We propose that corporations should be subject to a legal obligation to identify and internalise their social costs or negative externalities. Our proposal reframes corporate social responsibility (CSR) as obligated internalisation of social costs, and relies on reflexive governance through mandated hybrid fora. We argue that our approach advances theory, as well as practice and policy, by building on and going beyond prior attempts to address social costs, such as prescriptive government regulation, Coasian bargaining and political CSR.