"Using matched employer-employee-contract data for Portugal – a country with near-universal union coverage – we find evidence of a sizable effect of union affiliation on wages. Gelbach's (2016) decomposition procedure is next deployed to ascertain the contributions of worker, firm, match, and job-title heterogeneity to the union wage gap. Of these the most important is the firm fixed effect, followed at some distance by union workers gaining from elevated job titles and/or more generous promotion policies. For its part, unobserved worker quality plays only a very weak role, while there is even less suggestion that improved match quality bolsters the union premium."

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