424 L. van Waas, S. Jaghai with ‘avoiding discrimination in matters relating to nationality’55 and explicitly provides that ‘Each State Party shall be guided by the principle of non-discrimination between its nationals, whether they are nationals by birth or have acquired its nationality subsequently’.56 From this it could be concluded that international law is giving off mixed messages about the legitimacy of rules under which the deprivation of nationality operates unequally. Looking more closely, the UN Human Rights Committee explains that not every form of differential treatment constitutes discrimination.57 Severe national security risks and the fact that dual citizens are not prone to being rendered stateless in the way that mono citizens are could justify differential treatment, if such differential treatment has a legitimate aim and if it is proportionate. Barak clearly sets out the four components of the proportionality test: (1) It is designed for a proper purpose (2) the measures undertaken to effectuate such a limitation are rationally connected to the fulfilment of that purpose (3) the measures undertaken are necessary in that there are no alternative measures that may similarly achieve that same purpose with a lesser degree of limitation and (4) there needs to be a proper relation (proportionality stricto sensu or ‘balancing’) between the importance of achieving the proper purpose and the social importance of preventing the limitation on the constitutional right.58 A way to resolve the question of international law’s apparent ‘mixed messages’ on this issue could then be to explore whether the unequal use of nationality deprivation as it is emerging today in the counter-terrorism context would pass this test. The purpose of nationality deprivation as a counter-terrorism measure, as outlined in policy debates, is to strengthen national security by acting as a deterrent or preventative instrument and/or to punish those who turn their back on the state. While both the purposes of protecting security and effecting punishment are ‘proper’ aims and functions of the state, the further criteria of the proportionality test may pose a problem to the legitimacy of deprivation of nationality in pursuit of these aims—especially where it is of unequal application among citizens. For instance, will citizenship stripping actually effectuate either purpose if only a small sub-set of citizens is subject to the measure—i.e. what about the mono nationals and nativeborn citizens that pose a threat to national security? And, if deprivation of nationality is used as an added punishment for some citizens, but not others, how is this to be understood in light of the legal principle of ne bis in idem (to not be punished twice for the same crime)?59 55 Preamble, European Convention on Nationality. Art. 5(2), European Convention on Nationality. 57 UN Human Rights Committee (1989), p. 3. 58 Barak (2012), p. 3. 59 Note also that neither the 1961 Convention nor the ECN permits states to revoke citizenship of persons as a response to an ordinary crime. Both treaties refer to ‘conduct seriously prejudicial to the vital interests of the State Party’ as a ground for deprivation, calling further into question whether the purpose of punishment as such is legitimate for denationalisation. 56 123