Trade unions have an important role in both the legal establishment of the rights of migrant workers and the implementation of these rights. However, unions have faced dilemmas such as supporting or resisting immigration policies, including or excluding immigrants from unions, treating all workers equally within their organizational structures, or developing unique policies and strategies for migrant workers. By focusing on the relationship between unions and migrant workers, this study aims to reveal the different policies and activities of unions towards migrant workers among social rights and dilemmas. International trade unions promoting a rights-based approach, equal treatment and anti- discriminative policies towards migrant workers, advocating that migrants should be considered as “workers” rather than “migrant workers”. On the other hand, it has been concluded that the heterogeneous structure of migrant workers, the capacity of unions to influence social and economic policies at the national level, their philosophical and organizational structures, economic and labour market conditions in the country, public discourse towards immigrants, and the financial power of the unions are effective and determinant in the orientation of the unions to migrant workers.