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Data from plumbing and pipefitting union locals are used to measure the effect of union organizing strength on the wages of high-skilled and semi-skilled nonunion workers. We find that increases in union strength are associated with higher wages for nonunion journeymen. However, the wages of lower skilled, nonunion journeymen helpers are not related to our measures of union recruitment power. These results are consistent with the organizing tactic of labor stripping where skilled nonunion workers are convinced to leave their nonunion employers and join the union. Greater union strength is not associated with higher wages for union journeymen. Rather, these workers derive increased employment opportunities where the union is strong. Our results suggest that the union threat effect is different in the construction industry where unions develop unique strategies due to the nature of the industry. Key words: union threat effect, union-nonunion wage gap, construction