Existing studies of Association of Southeast Asian Nations (ASEAN) states' engagement with migrant worker rights focus on the experience of such workers from gender, labour and security perspectives. As such, these studies are yet to consider the broader impact of migrant worker rights on the process and nature of cooperation between ASEAN members. This article addresses this gap by framing migrant worker rights within the broader human rights socialization ongoing within Southeast Asia, driven by both members of ASEAN and external stakeholders. It argues that, contrary to many existing accounts of norms as creating shared commitments, migrant worker rights have led to considerable contestation, often driven by diverging national approaches to the issue. This article examines the impact of migrant worker rights norms on Thailand, the largest labour-recipient state in ASEAN. It asserts that Thailand's diverging experience is caused by the lack of norm precision, resulting in the applicatory contestation of such norms.