National Labor Relations Board (NLRB): The NLRB works to protect employees' rights to organize and to determine whether to have union representation. The agency also tries to prevent and change unfair labor practices committed by private sector employers and unions.
The National Labor Relations Board is an independent federal agency vested with the power to safeguard employees' rights to organize and to determine whether to have unions as their bargaining representative.
Finding information about unions can be daunting. In order to find information about unions you may want to use the industry you are researching. Here is what the Library of Congress suggests from http://www.loc.gov/pictures/item/tgm005736/:
Include activities and structures;
Include the Industry:
Related aspects of unions: