Due to institutional pressures faced by companies in their business environment, this paper investigates how sustainability certification adoption affects global suppliers' competences. Using multiple case studies, managers of 20 export-oriented firms were interviewed, and secondary data were collected and analysed through inductive content analysis. Findings show normative and mimetic pressures as central for sustainability implementation by coffee suppliers. Additionally, we found that as a result of suppliers' sustainability improvement in their own operations, during the certification adoption, new competences emerged going beyond the triple bottom line dimensions, including improvements in aspects of institutional dimension of sustainability. In contrast to previous research in supply chain sustainability that emphasises coercive pressures, this paper demonstrates the role of normative and mimetic institutional pressures in developing new supplier competences. In doing so, we draw on the role of certification adoption in influencing global suppliers and hence sustainability throughout the supply chain.