Voluntary certification schemes aimed at assuring producer compliance with a set of sustainability criteria have emerged as market-based instruments (MBIs) of sustainability governance. However, the impacts they tackle can be part of a complex arena of socio-environmental conflict, where values and powers of business and local actors compete. Legitimacy of these schemes not only results from compliance by business actors; but also depends on acceptance by local actors affected by, or resisting the industries that these mechanisms aim to govern. This paper explores the influence of different local actors' values and powers on legitimacy granting or contestation by local actors during national processes of sustainability criteria development. We analyse the case of the Roundtable on Sustainable Palm Oil (RSPO) in Colombia using an approach that combines concepts of ecological economics and political ecology with the legitimacy literature based on critical sociology. In Colombia, the palm oil industry led the initiative to implement certification under national interpretation of RSPO principles and criteria. However, the national interpretation process revealed power asymmetries among stakeholders and clashes between their different values. This resulted in strong contestation of RSPO legitimacy by local actors who resist expansion of oil palm cultivation.