Members of most labor unions in the United States pay a portion of their wages to their local to support the union's internal government, pay for any legal representation, and contribute to a strike fund. Many unions also spend some of their members' dues to lobby and campaign for politicians they support.
All active members of a given union pay dues, which are sometimes source deducted by the employer and remitted directly to the international office of the union, which keeps a portion and sends the rest on to the local union office. Just as common is the local union collects the dues and remits a portion to the international union.
In collective bargaining agreements, the wage level is typically prescribed on the basis of seniority and attained education and rank. For instance, a journeyman makes more money than an apprentice. The dues are typically a percentage of gross wages but may also involve set rates per hour plus contributions to certain funds operated by the international, or local union office.