Columbia subject headings:
Labor laws and legislation--United States--History.
Labor unions--Law and legislation--Europe--History.
Labor unions--Law and legislation--United States--History.
Labor unions--Social aspects--United States.
Harvard subject headings:
Labor laws and legislation--United States--History
Labor unions--Law and legislation--Europe--History.
Labor unions--Law and legislation--United States--History.
Labor unions--Social aspects--United States.
Princeton subject headings:
Labor laws and legislation--United States--History.
Labor unions--Law and legislation--Europe--History.
Labor unions--Law and legislation--United States--History.
Labor unions--Social aspects--United States.