CMW/C/GC/2 4, complements article 9, paragraph 1, of the International Covenant on Civil and Political Rights, adding that migrant workers and members of their families shall not be subjected “individually or collectively” to arbitrary arrest or detention. In order not to be arbitrary, arrest and detention of migrant workers and members of their families, including those in an irregular situation, must be prescribed by law, pursue a legitimate aim under the Convention, be necessary in the specific circumstances and proportionate to the legitimate aim pursued. 24. The Committee considers that crossing the border of a country in an unauthorized manner or without proper documentation, or overstaying a permit of stay does not constitute a crime. Criminalizing irregular entry into a country exceeds the legitimate interest of States parties to control and regulate irregular migration, and leads to unnecessary detention. While irregular entry and stay may constitute administrative offences, they are not crimes per se against persons, property or national security. 14 25. Although article 16, paragraph 4, does not define the permissible grounds for detention, it states that migrant workers and members of their families shall not be deprived of their liberty, except on such grounds and in accordance with such procedures as are established by law. Furthermore detention must be prescribed by law, pursue a legitimate aim under the Convention, be necessary in the specific circumstances, and proportionate to the legitimate aim pursued. 26. In the Committee’s view, any custodial or non-custodial measure restricting the right to liberty must be exceptional and always based on a detailed and individualized assessment. Such assessment should consider the necessity and appropriateness of any restriction of liberty, including whether it is proportional to the objective to be achieved. The principle of proportionality requires States parties to detain migrant workers only as a last resort, and to give preference to less coercive measures, especially non-custodial measures, whenever such measures suffice to achieve the objective pursued. In all such cases, the least intrusive and restrictive measure possible in each individual case should be applied. 27. Administrative detention of migrants that is initially lawful and non-arbitrary may become arbitrary if it continues beyond the period for which a State party can provide proper justification. To prevent such a situation from occurring, a maximum period of administrative detention shall be established by law, upon expiry of which a detainee must be automatically released in the absence of such justification. Administrative detention must never be unlimited or of excessive length. The justification for keeping a migrant worker detained shall be reviewed periodically to prevent prolonged and unjustified detention, which would be considered arbitrary. Preventive detention of migrant workers often leads to prolonged detention based on vague criteria. Therefore, such detention should be imposed only following an individual assessment in each case and for the shortest time possible, in compliance with all procedural safeguards provided for in article 16 of the Convention. In cases where an expulsion order cannot be executed for reasons beyond the detained migrant worker’s control, he or she shall be released in order to avoid potentially indefinite detention. 28. Article 16, paragraph 5, requires States parties to inform migrant workers and members of their families who are arrested of the reasons for their arrest at the time of arrest and, as far as possible, in a language they understand. Moreover, they must be 14 See report of the Special Rapporteur on the human rights of migrants to the Human Rights Council (A/HRC/20/24), para. 13. 9