"It has been widely assumed that type-of-contract segmentation represents a strong structural constraint on trade union growth. The analysis of a sample of the Spanish workforce shows, however, that the effect of contract type on union membership is not statistically significant once the availability and performance of local union representatives are introduced in the explanatory model. Additionally, the worker's participative potential, as indicated by his/her social and political capital, is also found to be a major explanatory factor. These findings are placed in comparative perspective and discussed in relation to possible union revitalisation strategies."

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