The EU’s power is expanding, calling for reassessments of its normative legitimacy. This article proposes a novel criterion for assessing the EU’s legitimacy: symmetry in the delegation of power. We illustrate the usefulness of this criterion through an analysis of the European border regime. Existing analyses of the border regime have tended to dismiss it as weak and intergovernmental. We show, to the contrary, that it is both strong and weak. The EU wields significant power in border control but lacks power altogether in immigration policy. This asymmetry has rendered the EU incapable of discharging the moral responsibilities that arise in migration control, posing a novel legitimacy challenge. Finally, we argue that the symmetry criterion generalises and can shed light on the EU’s legitimacy beyond the area of migration.