in line with the general principle that a person may not be tried for conduct that was not an offence at the time the conduct occurred.103 As a safeguard against statelessness or other adverse consequences of withdrawal of nationality, where a new ground for loss or deprivation of nationality is introduced in national law, the State should include a transitional provision to prevent an individual from losing their nationally due to acts or facts which would not have resulted in loss or deprivation of nationality before the introduction of a new ground. Withdrawal of nationality must always be proportionate to a legitimate aim The principle of proportionality is reflected in numerous international human rights instruments, including international and regional human rights treaties.104 For withdrawal of nationality to be proportionate, measures leading to the withdrawal of nationality should “serve a legitimate purpose that is consistent with … the objectives of international human rights law” and be the least intrusive means necessary to achieve the aim pursued by the State.105 Therefore, the consequences of loss or deprivation of nationality must be weighed against the aim pursued.106 The impact of withdrawal of nationality on the individual’s ability to access and enjoy other human rights (in particular those discussed in these Guidelines) should be taken into consideration. In addition, the aim pursued must be legitimate in that it must not be to punish a person for asserting rights such as the right to freedom of expression or association by withdrawing nationality. The question of whether a person is in possession of another nationality is relevant to the assessment of whether loss or deprivation of nationality is proportionate to the aim pursued by the State because it is a key factor in determining the consequences for the individual concerned. If the person is not in possession of another nationality, the withdrawal of nationality will result in statelessness.107 Even where a person is in possession of another nationality or may be able to (re-) acquire another nationality, any loss of the right to reside in the State in question will result in the loss of all the rights which attach to residence. States should therefore ensure that there are no less intrusive alternatives to achieve the relevant aim before withdrawal of nationality occurs. Given the severe consequences of statelessness, withdrawal of nationality 103 See e.g., Case of Expelled Dominicans and Haitians v Dominican Republic, 28 August 2014, Inter-American Court of Human Rights, Series C No. 282, para. 298. 104 See e.g., Yutaka Arai-Takahashi, ‘Proportionality’ in Dinah Shelton (ed), The Oxford Handbook of International Human Rights Law (Oxford University Press 2013), DOI: 10.1093/law/9780199640133.003.0020. 105 See e.g., Rottmann v Freistaat Bayern, Case C-135/08, [2010] ECR I-01449, https://www.refworld.org/cases,ECJ,4be130552.html, para. 56; Human Rights Council, Human rights and arbitrary deprivation of nationality: Report of the Secretary-General, 19 December 2013, A/HRC/13/34, para. 25; and Human Rights Council, Human rights and arbitrary deprivation of nationality: Report of the SecretaryGeneral, 19 December 2013, A/HRC/25/28, para. 4. 106 International Law Commission, Draft Articles on the Expulsion of Aliens with commentaries, Yearbook of the International Law Commission, 2011 Vol. II (Part Two), https://www.refworld.org/docid/5539ef8e4.html, Article 8. 107 See e.g., Rottmann v Freistaat Bayern, Case C-135/08, [2010] ECR I-01449, https://www.refworld.org/cases,ECJ,4be130552.html, para. 57. UNHCR > GUIDELINES ON STATELESSNESS NO.5 29

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