"The labour market dualisation theory claims that labour unions bargain against the interests of temporary workers and that they foster inequalities between temporary and permanent employees. Conversely, the industrial relations literature argues that unions commonly follow solidaristic strategies towards outsiders. This study contributes to the literature by analysing unions' associations with temporary workers' hourly wages and the wage gap between permanent and temporary workers in Spain: one of the most prominent examples of labour market dualisation. By analysing cross-sectional surveys, unions' influence through works councils, collective agreements and union density are studied during a period of economic growth (2006–2007) and a period of recession (2008–2010). Results show that there is generally no association between these three institutions and wage differences between permanent and temporary workers. The associations with temporary workers' wages are insignificant or positive during both the period of economic growth and the period of recession."

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