This paper critically examines the extensive scholarship on the discretionary power of street-level bureaucrats (Lipsky 1980, Dubois 2010, Evan & Harris 2004) within the realm of migration policy implementation studies (Gilboy 1991, Weber 2003, Alpes & Spire 2014, Infantino & Sredanovic 2022, Eule et al. 2020). It underscores the role of an often-overlooked group of professionals directly involved in border control activities but who do not represent the State nor have an official mandate on migration issues: railway workers (RW). By focusing on the discretion exercised by non-State actors (Darling 2022, Infantino 2017) and their relational power, I argue that RW's discretionary decisions on who can cross the French-Italian border by train, and under what conditions, play a crucial role in shaping the practical effects of the border regime (De Genova 2010). By considering the ongoing organizational reform of the national railway company (SNCF), and by comparing two different sets of practices of these RW, this study highlights how their discretion is relational, influenced by various factors including their perception of accountability and sanctions, the importance of higher principles, their relationship with line management, employment stability, personal and professional resources (family, unionized colleagues), and their experiences in sensitive encounters with exiles and police officers.