Voluntary sustainability standards (VSSs) are non-mandatory criteria designed to foster sustainable practices throughout the global supply chain. These standards are particularly prevalent in the agri-food sector, where they aim to support wider public policy objectives such as sustainable food production, animal welfare, healthy lifestyle, and labour conditions. Significant challenges arises from the fact that VSSs, despite their voluntary nature, they often impose mandatory effect in the global supply chain. They also often lack easily-identifiable features of the product themselves. These creates systematic problems for the global food trade system, where conventional regulation address governmental measures on goods with specific inherent characteristics that can be clearly identified in the final product. This article explored the interrelationship among private VSSs, national regulations and international treaties within the agri-food industry. It highlights ambiguity surrounding the regulatory framework for VSSs under the WTO law, noting the absence of a consensus on how relevant provisions should be interpreted. Despite the diversity among various VSSs, VSSs, this article argues for the potential for harmonization and equivalence among VSSs. By aligning various VSSs and with technical regulations, it is possible to strike a balance between trade liberalization and promotion of sustainable practices.