Union Organization and Activity by 
The Challenge of Interracial Unionism: Alabama Coal Miners, 1878-1921 by 
The Decline of US Labor Unions and the Role of Trade by 
Farewell to the Factory - Autoworkers in the Late Twentieth Century by 
Hard Work: Remaking the American Labor Movement by 
Managed Professionals: Unionized Faculty and Restructuring Academic Labor by 
Organized Labor and American Politics, 1894-1994 by 
State of the Union: A Century of American Labor by Opposing Viewpoints presents articles, reference books, videos, audio on a variety of social issues including labor unions, offshoring, collective bargaining, and more.
One way to locate the history of unions is to go to their web sites; most include some background history. Here are some examples:
