Under what conditions do immigration policies lose their perceived legitimacy, not because of who immigrants are, but because of how immigration is governed? This paper develops a norms-based model of immigration legitimacy that centers on public judgments on procedural fairness. Citizens evaluate immigration through expectations of rule adherence, reciprocity, transparency, and accountable authority. When either immigrants or governing institutions violate these norms, support declines even in the absence of strong cultural or economic threat. To test this model, the study fields two linked survey experiments in the United States, Germany, South Korea, and Singapore, a set of cases that vary in regime type, institutional design, and migration experience. A paired profile conjoint identifies the weight of fairness cues in evaluations of individual immigrants. A vignette experiment examines how legitimacy shifts when immigration decisions involve executive overreach, external pressure, or procedural neglect. Across contexts, fairness cues consistently increase support, and procedural violations reduce legitimacy. The findings show that immigration attitudes reflect concerns not only about who enters, but about whether immigration is governed in ways that meet widely shared expectations of fairness and rightful authority.