Following decades of concern about unsustainable forest management practices, forest certification was developed in the 1990s to become an influential global forest governance approach. 25 years since its inception, forest certification is under attack, with questions raised regarding its legitimacy and efficacy in driving sustainable forest management. Recognising forest certification as a complex and dynamic boundary-spanning regime, understanding the impact of diverse boundaries on forest certification is essential to address escalating conflict and enable the improved design of forest certification systems. This paper empirically explores the implementation of a forest certification regime using a Forest Stewardship Certification pesticide derogation process. The case shows how competing boundaries place considerable pressure on the effectiveness and sustainability of the global certification regime. Embedded local interests and contested institutional claims hardened the boundaries between interests across the policy regime, weakening connections and hence weakening opportunities to find common solutions.