The Walter P. Reuther Library of Labor and Urban Affairs houses a significant collection of materials related to labor history in the United States. The collection includes archives, visual materials, oral histories, and photographs and other materials documenting the U.S. labor movement. Unions whose archives are housed at the Reuther include the United Auto Workers (UAW), the American Federation of Teachers, the AFL-CIO, and many, many others.
Manuscript collections at the Reuther can be searched here.
The finding aid for the Oral History Collection is available here.