Ethnographic approaches to transnational legal conflicts (TLCs) can provide key insights into the material and symbolic manifestation of the authority of international organisations (IOs) within global governance. TLCs emerge due to the differing pursuits and ambitions of actors in a pluralistic global society. In global governance, the multiplication of international institutions and the fragmented legal frameworks to which they refer raise questions as to the legitimation of IOs’ authority. This contribution builds on ethnographic observations of the TLCs around migrant rescues at the external maritime border of the EU in the Central Mediterranean. The emergence of the Libyan Search and Rescue Region (SRR) in the International Maritime Organization’s Global Search and Rescue Plan in June 2018 legitimised European authorities’ handing over of responsibility to Libyan authorities to coordinate the rescue of migrants and to thus disembark survivors in Libya. This, in turn, clashed with the international principle of non-refoulement and the duty to disembark rescued people in a place of safety according to the 1979 Convention on Maritime Search and Rescue. By describing the dilemmas posed to NGOs involved in rescues of migrants in the Libyan SRR, this contribution shows how IOs’ transnational authority materialises in the on-site hierarchisation of legal provisions within TLCs.