Columbia subject headings:
Labor unions--United States--Bibliography.
Labor unions--United States--Directories.
Labor unions--United States--History.
Harvard subject headings:
Bibliographies.
Directories.
Labor unions--United States--Bibliography.
Labor unions--United States--Directories
Labor unions--United States--History
Princeton subject headings:
Directories.
Labor unions--United States--Bibliography.
Labor unions--United States--Directories.
Labor unions--United States--History.