A/59/377 enjoyment of civil, political, economic, social and cultural rights of non-citizens. It stresses measures relating to labour and employment rights of non-citizen workers, as well as guarantees with regard to non-citizens who are detained or imprisoned. 37. The increasingly prevalent and disturbing practice of administrative detention of undocumented immigrants entails the violation of the principle of nondiscrimination with regard to migrants with irregular status. Indeed, when these individuals are arrested by police and sent to detention centres without the possibility of appealing to a court to determine whether their detention is lawful, they are being discriminated against in the exercise of their basic right to freedom and legal security. At the same time, they are arbitrarily denied the right to effective recourse against their detention by police. This situation has become widespread as States have adopted and applied special legislation to combat terrorism, given that such legislation restricts or suspends the procedural guarantees that every detainee should enjoy. 38. A State may take action against persons who enter its territory without authorization, but such measures must respect the human rights of the persons detained, regardless of their migration status. Efforts are being made to have international human rights law establish the boundaries outside of which any detention, whether administrative or judicial, would be considered arbitrary. The existence of a rapid and effective appeals procedure entails the assumption of a guarantee in any situation where a detention has not been ordered by a judge, especially in cases of immigration-related detentions. Consequently, a judge should be able to monitor the material lawfulness of administrative detention and to decide whether or not it is in accordance with law, even when the detention occurs in the transit area of an airport. The Special Rapporteur considers that legal assistance must be available in such cases. 39. At the institutional level, the Working Group on Arbitrary Detention is paying special attention to this issue, both in its visits and in individual cases.8 In her report to the Commission on Human Rights at its fifty-ninth session (E/CN.4/2003/85), the Special Rapporteur included a study on the human rights of migrants deprived of their liberty. In that report, she expressed her concern at the lack of guarantees to protect human rights during administrative detention of migrants with irregular administrative status, especially for purposes of expulsion (ibid., paras. 65-71). During her official missions, the Special Rapporteur has visited detention centres for immigrants with irregular status in order to determine whether adequate mechanisms were in place for submitting complaints and to determine what are the implications of such centres being managed by the private sector. 40. In brief, the importance of the principle of equality and non-discrimination in the formation of international human rights law relating to migration is reflected in the general comments and general recommendations of the bodies established under the aforementioned conventions. 41. At the regional level, the Inter-American Court of Human Rights has expressed similar views on the principle of equality and non-discrimination in its Advisory Opinion OC-18/03. The Court adds that States must respect and ensure the full and free enjoyment of human rights in the light of the general principle of equality and non-discrimination. Hence, if a State fails to comply with this general obligation and applies any discriminatory treatment, its non-compliance entails the international responsibility of the State (paras. 85-96). 13