International Convention on the Protection of the Rights of All Migrant Workers and their Families, 1990
Article 27:
1. With respect to social security, migrant workers and members of their families shall enjoy in the State of employment the same treatment granted to nationals in so far as they fulfil the requirements provided for by the applicable legislation of that State and the applicable bilateral and multilateral treaties. The competent authorities of the State of origin and the State of employment can at any time establish the necessary arrangements to determine the modalities of application of this norm.
2. Where the applicable legislation does not allow migrant workers and members of their families a benefit, the States concerned shall examine the possibility of reimbursing interested persons the amount of contributions made by them with respect to that benefit on the basis of the treatment granted to nationals who are in similar circumstances.