Equal treatment is a fundamental principle of contemporary constitutionalism, which may challenge migration law, since the latter reiterates the basic distinction between citizens and aliens as well as among different categories of migrants.   The contribution shows that constitutional law is based upon an – usually invisible – inequality threshold, which becomes evident when we consider rules on entry into the territory and the diverse distinctions among different migration statuses. Limits of equal treatment permeate the restrained case law of the ECtHR and define the judicial caution of the CJEU and the EU legislature in the interpretation and design of the Charter of Fundamental Rights and secondary law.