Union Density and Relative Wages: What is the Relationship?

ABSTRACT: This paper examines the impact of union density on relative wages under decentralised bargaining settings. Whilst, traditionally, empirical studies have focused on the impact of union status on wages (either at the individual or at the plant level), here it is argued that local trade union density can have an independent (positive) effect on wages. This occurs through the threat of collective action and the ability of the union to impose costs onto employers. First, a Nash bargaining model is presented under efficient-bargaining settings, and a wage-membership equation is derived. Wages are shown to be an increasing and convex function of union membership. Second, an empirical specification of the wage-membership equation, suitable for estimation, is obtained and fitted to establishment-level data for the Italian metal-mechanical engineering industry. A positive monotonic relationship between wages and union density is detected. Furthermore, wages are shown to be increasing with union density even where no formal local bargaining agreement is in force, thus suggesting that “union-threat” effects might be relevant.