The research applies Siemsen et al.'s Constraining Factor Model (CFM) to sustainable supply chain management. This involves two case studies, one in offshore wind farm development and another in heavy manufacturing. In both, there was an inability to maximise improved environmental performance. Analysis reveals the constraining factors, which CFM defines either in terms of motivation, opportunity and ability. Exogenous opportunity factors are found to constrain the focal firms and their supply chains maximising improved macro-scale environmental performance. These include regulatory, macro-economic and socio-psychological (behavioural) factors.