We study the earning structure and the equilibrium assignment of workers to firms in a model where workers have social preferences and skills are perfectly substitutable in production. We allow firms to offer long-term contracts and for frictions in the labour market in the form of mobility costs. For low moving costs between firms, heterogeneous productivities lead to widespread workplace skill segregation and the whole market wage dispersion is explained by between firm differences.

In a labor market with intermediate levels of mobility costs, segregation is more moderate and wage dispersion arises both within and across firms. For high levels of moving costs, the whole wage dispersion is within the firm and becomes zero when the moving costs are sufficiently high. We show that long-term contracts in the presence of social preferences associate within-firm wage dispersion with novel internal labor market features such as a dynamic form of wage compression, gradual promotions an dwage non-monotonicity.