Monopsony and the Wage Effects of Migration

If labour markets are competitive, migration can only affect native wages via marginal products. But under imperfect competition, migration may also increase wage mark-downs—if firms have greater monopsony power over migrants than natives, but cannot perfectly wage discriminate. While marginal products depend on relative labour supplies across skill cells, mark-downs depend on migrant concentration within them. This insight can help rationalise empirical violations of canonical migration models. Using US data, we conclude that migration does increase mark-downs: this expands aggregate native income, but redistributes it from workers to firms. Policies which constrain monopsony power over migrants can mitigate these adverse wage effects.