C143 Migrant Workers (Supplementary Provisions) Convention, 1975Article 9
1. Without prejudice to measures designed to control movements of migrants for employment by ensuring that migrant workers enter national territory and are admitted to employment in conformity with the relevant laws and regulations, the migrant worker shall, in cases in which these laws and regulations have not been respected and in which his position cannot be regularised, enjoy equality of treatment for himself and his family in respect of rights arising out of past employment as regards remuneration, social security and other benefits.
2. In case of dispute about the rights referred to in the preceding paragraph, the worker shall have the possibility of presenting his case to a competent body, either himself or through a representative.
3. In case of expulsion of the worker or his family, the cost shall not be borne by them.
4. Nothing in this Convention shall prevent Members from giving persons who are illegally residing or working within the country the right to stay and to take up legal employment.
Somebody quote an ILO convention, particularly the 9th article and give decision to an application, Malaysia has not rectify this one, so it has no effect to the general rule of an illegal contract is VOID.