Certification is widely seen as an innovative strategy for dealing with environmental problems in supply chains. As the number of labels available in the fisheries sector has increased, each with its own framing of sustainability, questions are being asked about their credibility. In tuna fisheries, contrasting approaches have led to conflict over, among other things, the credibility of competing labels. This paper investigates one such conflict between the Dolphin Safe and the Marine Stewardship Council certification schemes in the West and Central Pacific. It looks at how key practices like scientific rigour, inclusiveness, transparency/openness, impartiality/independence and impact contribute to label credibility and explains the importance of authority in understanding how certification schemes maintain influence within global production networks. The results demonstrate that despite substantially different levels of credibility within these networks, the application of an environmental standard is more connected to the authority of the standard setter than the credibility of the label. The paper concludes that understanding the more nuanced role of authority, both with and without credibility, offers new insights into the wider dynamics that shape environmental regulation in global production networks.