A/HRC/10/34 page 17 hampered by the effects of deprivation of nationality. States may therefore be required to adopt flexible rules for evidence, which for instance allow the person concerned to provide witness testimony or resort to various sources of documentary evidence. 60. In the context of the avoidance of statelessness, arbitrary denial of nationality is just as grave as arbitrary deprivation of nationality. The Executive Committee of UNHCR has therefore encouraged States “to consider examining their nationality laws and other relevant legislation with a view to adopting and implementing safeguards, consistent with fundamental principles of international law, to prevent the occurrence of statelessness which results from arbitrary denial or deprivation of nationality” (emphasis added).10 61. Nationality can be acquired automatically by operation of law, at birth or at a later stage, or as a result of an act of the administrative authorities. States enjoy a degree of discretion with regard to the criteria governing acquisition of nationality but these criteria must not be arbitrary. In order not to be arbitrary, denial of access to a nationality must be in conformity with domestic law. It must comply with procedural standards. At a minimum, a decision must be issued with reasons in writing and be subject to review by an independent authority. It must comply with substantive standards, in particular the principle of proportionality. As with arbitrary deprivation of nationality, international law has developed detailed standards governing denial of nationality, in particular where it is based on discriminatory grounds or where it results in statelessness. 62. In establishing general rules for acquisition of nationality at birth or later in life, it is legitimate to differentiate between persons who have specific links with the State such as birth on the territory, descent, residence or marriage to a national, and those who do not. However, when setting criteria for acquisition of nationality, States must not discriminate against persons concerned, in particular on grounds of race, colour, gender, religion, political opinion or national or ethnic origin, as such discrimination would constitute arbitrary denial of acquisition of a nationality. Article 9 of the Convention on the Elimination of All Forms of Discrimination against Women prohibits distinctions between men and women with regard to acquisition of nationality and in relation to acquisition of nationality by their children. Discrimination on the grounds of race, colour or ethnicity falls under the scope of the Convention on the Elimination of All Forms of Racial Discrimination. 63. With regard to the acquisition of nationality, the Committee on the Elimination of Racial Discrimination recommended that States parties to “ensure that particular groups of non-citizens are not discriminated against with regard to access to citizenship or naturalization, and to pay due attention to possible barriers to naturalization that may exist for long-term or permanent residents” and to “take into consideration that in some cases denial of citizenship for long-term or permanent residents could result in creating disadvantage for them in access to employment and social benefits, in violation of the Convention’s anti-discrimination principles”.11 The Human Rights Committee, in its general comment No. 24 has stated: “No discrimination with 10 Executive Committee conclusion No. 106 (LVII) - 2006, para. (i). Report of the independent expert on minority issues, Gay McDougall, 28 February 2008, A/HRC/7/23. 11 CERD, general recommendat1ion XXX.