What is the fine-grained topic of the following text: His campaign is also supported by the United Aerospace Workers Local 887, the International Association of Bridge, Structural, Ornamental and Reinforcing Iron Workers Local 416 and Local 433, the United Association of Plumbers, Pipefitters and Welders Local 761, the International Brotherhood of Electrical Workers Local 40, Sheet Metal Workers Local 105, and the United Steelworkers Local 675. Only return the topic.
Union support for a political campaign