Transparency lies at the heart of canonical theories of international negotiations and institutions—yet it is rarely directly measured or explained. This paper explores the potential downsides of transparency reforms in intergovernmental negotiations and institutions. We argue that as formal international meetings open up to the public, negotiators face incentives to shift deliberations to more informal and opaque venues, especially for sensitive and domestically contested issues. To test when and why this occurs, we present new data on three decades of intergovernmental negotiations in the Council of the European Union (1990–2019), and in particular the use of informal breaks where no minutes are taken. We find that recourse to such breaks—especially at lunch time—has increased substantially, and that ministers often take these opportunities to discuss controversial topics. We deploy quantitative and qualitative analyses to show that variations in informal breaks correlate both with institutional enhancements to transparency and with specific concerns over antagonistic political mobilization at home, notably in the form of Euroscepticism. These findings challenge received positive and normative theories about transparency in international institutions, and contribute to the literature on informal governance, negotiation studies, EU politics, and the transnational democratic deficit.

透明度是国际谈判和机构的规范理论的核心，但很少被直接衡量或解释。本文探讨了透明度改革在政府间谈判和机构中的潜在弊端。我们认为，随着正式的国际会议向公众开放，谈判代表面临将审议转移到更非正式和不透明的场所的诱因，特别是对于敏感和国内有争议的问题。为了测试这种情况发生的时间和原因，我们提供了有关欧盟理事会三十年政府间谈判（1990-2019 年）的新数据，特别是使用不做会议记录的非正式休息。我们发现，利用这种休息时间——尤其是在午餐时间——已经大大增加，部长们经常利用这些机会讨论有争议的话题。我们部署了定量和定性分析，以表明非正式休息的变化既与透明度的制度增强有关，也与对国内对抗性政治动员的具体担忧有关，特别是以欧洲怀疑主义的形式。这些发现挑战了关于国际机构透明度的积极和规范理论，并为非正式治理、谈判研究、欧盟政治和跨国民主赤字的文献做出了贡献。