Thus, even though the formulation of such laws or practices may seem neutral, they may have negative effects in the practice. Among the different occasions that the Court has had to rule on the principle of equality and non-discrimination, Advisory Opinion No. 18 (2003) was paradigmatic because it was the first time the Court acknowledged that the right to equality and non-discrimination formed part of jus cogens.38 Thus, even though all States have the obligation to respect the Convention-based guarantees, without distinction, the principle “may be considered peremptory under general international law, inasmuch as it applies to all States, whether or not they are party to a specific international treaty, and gives rise to effects with regard to third parties, including private individuals.”39 30. Under Advisory Opinion OC-18/03, the State of Mexico consulted the Court on the possible restriction by the State of the enjoyment of the labor rights of undocumented migrant workers owing to their irregular migratory situation. In this context, the Court separated the concepts of “distinction,” which includes the differentiated treatment that is compatible with international standards, from “discrimination,” which refers to any exclusion, restriction or privilege that is not objective and reasonable.40 31. In principle, the restriction of rights may be justified when two basic and essential requirements are met: the restriction must be based on a specific legal provision and be applied proportionately.41 The application of this general principle is governed by the peculiarities of each right analyzed, in light of the international treaty that guides the analysis of the monitoring entity, in the case of the Inter-American Court, in particular the American Convention. 32. Allegations of the violation of the right to equality and non-discrimination call for a specific analysis of whether a differentiation was made based on criteria that were not objective and reasonable.42 Regarding the existence of differentiation, this stage of the analysis calls for the identification of a difference in treatment between individuals or groups in a similar situation. In the case of the criteria on which the differentiation is based, I note that the specific criteria based on which discrimination is prohibited in Article 1(1) of the Convention (race, color, sex, language, religion, political or other opinions, national or social origin, economic position, birth or any other social condition) are merely illustrative.43 33. As I explained in the preceding section, in the instant case, the distinction that regulated the restriction of Mr. Hendrix’s rights was his nationality, based on article 2(1) of the Guatemalan Notarial Code, which used this criterion to regulate access to the notarial profession, and not his domicile. It is evident that the criterion of “nationality” is Cf. Juridical Condition and Rights of Undocumented Migrants, Advisory Opinion OC-18/03, September 17, 2003. Series A No. 18, para. 97; Case of Atala Riffo and daughters v. Chile. Merits, reparations and costs. Judgment of February 24, 2012. Series C No. 239, para. 79; Case of Duque v. Colombia. Preliminary objections, merits, reparations and costs. Judgment of February 26, 2016. Series C No. 310, para. 91; Case of Vélez Loor v. Panama. Preliminary objections, merits, reparations and costs. Judgment of November 23, 2010. Series C No. 218, para. 248; Case of Nadege Dorzema et al. v. Dominican Republic. Merits, reparations and costs. Judgment of October 24, 2012. Series C No. 251, para. 225. 38 Thus, “all the norms of jus cogens necessarily generate obligations erga omnes. While jus cogens is a concept of material law, obligations erga omnes refer to the structure of their fulfillment by all the entities and all the individuals bound by them.” Cf. Juridical Condition and Rights of Undocumented Migrants, Advisory Opinion OC18/03, September 17, 2003. Series A No. 18. Opinion of Judge Cançado Trindade, para. 80. 39 Cf. Juridical Condition and Rights of Undocumented Migrants, Advisory Opinion OC-18/03, September 17, 2003. Series A No. 18, para. 84. 40 Cf. Case of Valencia Campos et al. v. Bolivia. Preliminary objection, merits, reparations and costs. Judgment of October 18, 2022. Series C No. 469. Separate opinion of Judge Nancy Hernández López and Judge Rodrigo Mudrovitsch, para. 39. 41 42 Cf. Case of I.V. v. Bolivia. Preliminary objections, merits, reparations and costs. Judgment of November 30, 2016. Series C No. 329, para. 240. Cf. Case of I.V. v. Bolivia. Preliminary objections, merits, reparations and costs. Judgment of November 30, 2016. Series C No. 329, para. 240. 43 8