A scholarly debate has recently emerged on the need to conceptualize justice at the EU level. In this debate, justice (and injustice) are seen as the key to understanding the EU project and, as such, as a unifying value of the EU. A connection is then required between the aspiration for justice and that of the overall legal architecture, or governance ambition of securing legitimacy for the European system. This paper seeks to go further and elucidate why it is helpful to analyze EU security regulation through the lens of justice as “non-domination” and how constitutionalism offers a useful framework for this process. In doing so, I explore the connection between the notions of justice and justification, and explain why their full comprehension enhances the legitimacy of the EU’s “Area of Freedom, Security and Justice” (AFSJ) project.