There are a number of different resources that may have information relevant to this research question. The U.S. Bureau of Labor Statistics releases an economic news item on Union Membership regularly which includes select worker characteristics of union affiliated employees, median weekly earnings, data by state, and more. The Office of Labor-Management Standards maintains a collective bargaining agreements file. There's also a Union Membership, Coverage and Earnings from the CPS database maintained by researchers at Georgia State, Trinity and Miami Universities. If you're looking for information on unions outside the US, the International Labour Organization has an Industrial Relations Data section.
These are just a few places to start. If you would like further assistance with this research, please contact the Business & Economics Librarian.
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