exercise of the right to nationality.147 In his survey of 2011, Peter Spiro noted criticisms from other UN treaty bodies of such provisions, and this criticism has continued, albeit inconsistently.148 Special rapporteurs have increasingly taken on discrimination on racial, ethnic and religious grounds in relation to nationality law and administration as belonging within their mandates, both as a specific theme,149 and as these issues affect other topics.150 The ECtHR has also begun to look beyond direct discrimination to consider indirect discrimination through provisions that disproportionately affect certain groups. In a case against Denmark, for example, the Court found that national legislation on the right to family reunification for the spouses of Danish citizens was discriminatory, since requirements in relation to the strength of ties to Denmark were more likely to affect naturalised citizens not of Danish origin.151 But it is again the Inter-American and African human rights mechanisms that have developed furthest the arguments condemning discrimination in the acquisition of nationality, not only in the law but also in its application, linking non-discrimination to the principle of equality before the law. As noted by Foster and Baker, the IACtHR affirmed the principle of non-discrimination as jus cogens in its 2003 Advisory Opinion on Legal Status and Rights of Undocumented Migrants.152 In the Yean and Bosico case, the Court asserted that ‘States must abstain from producing regulations that are discriminatory or have discriminatory effects on certain groups’.153 In the later case relating to Dominicans and Haitians expelled from the Dominican Republic to Haiti, the Court held that is for the State to prove that differentiated treatment does not entail a violation of the right to equal protection of the law, and fulfils the criteria of legitimate purpose and proportionality with the end sought.154 In 2023, the IACHR codified these principles in a comprehensive resolution on nationality and statelessness.155 147 Starting from UN Commission on Human Rights, ‘Resolution 1997/36: Human Rights and Arbitrary Deprivation of Nationality’ (11 April 1997) UN Doc E/CN.4/1997/36; most recently, UN Human Rights Council, ‘Resolution 32/5: Human Rights and Arbitrary Deprivation of Nationality’ (15 July 2016) UN Doc A/HRC/RES/32/5; see also UN Human Rights Council, ‘Resolution 53/16: The Right to a Nationality: Equality in Nationality Rights in Law and in Practice’ (24 July 2033) UN Doc A/HRC/RES/53/16. 148 Spiro (n 6) 727–30. Concluding Observations post-dating Peter Spiro’s 2011 article can be searched at Institute on Statelessness and Inclusion <https://database.institutesi.org/>, and include criticism on these grounds of Syria, Liberia, Dominican Republic, Bhutan and Qatar (among others). 149 G McDougall, ‘Report of the Independent Expert on Minority Issues: Minorities and the Discriminatory Denial or Deprivation of Citizenship’ (23 February 2008) UN Doc A/HRC/7/23; A Jahangir, ‘Interim Report of the Special Rapporteur on Freedom of Religion or Belief: Citizenship Issues and Religious Discrimination in Administrative Procedures’ (22 July 2008) UN Doc A/63/161; F de Varennes, ‘Report of the Special Rapporteur on Minority Issues: Statelessness: A Minority Issue’ 22 July 2018 (UN Doc A/73/205); ET Achiume, ‘Report of the Special Rapporteur on Contemporary Forms of Racism, Racial Discrimination, Xenophobia and Related Intolerance: Racial Discrimination in the Context of Citizenship, Nationality and Immigration Status’ (5 April 2018) UN Doc A/HRC/38/52, 2; S Mullally, ‘Report of the Special Rapporteur on Trafficking in Persons, Especially Women and Children: Refugee Protection, Internal Displacement and Statelessness’ (3 July 2023) UN Doc A/HRC/53/28. 150 M de Boer-Buquicchio, ‘Report of the Special Rapporteur on the Sale and Sexual Exploitation of Children, including Child Prostitution, Child Pornography and Other Child Sexual Abuse Material, on Her Visit to the Dominican Republic’ (5 January 2018) UN Doc A/HRC/37/60/Add.1, para 8 and recommendations; P Alston, ‘Report of the Special Rapporteur on Extreme Poverty and Human Rights on his mission to Mauritania’, 8 March 2017 (UN Doc A/HRC/35/26/Add.1) paras 45–46. 151 Biao v Denmark (2016) 64 EHRR 1, paras 93–94. See also E Ersbøll, ‘Biao v Denmark: Discrimination among Nationals’ (GLOBALCIT, 12 July 2016) <https://globalcit.eu/biao-v-denmark-discrimination-among-nationals/>. 152 Advisory Opinion OC-18/03: Juridical Condition and Rights of Undocumented Migrants (IACtHR, 2003) para 101, cited in Foster and Baker (n 4) 133–34. 153 Girls Yean and Bosico (n 19) para 141. 154 Expelled Dominicans and Haitians (n 45) para 316. 155 Resolution 2/23 on the Right to Nationality (n 54).