Columbia subject headings:
Labor unions--Political activity--Germany--History.
Labor unions--Political activity--Great Britain--History.
Labor unions--Political activity--United States--History.
Harvard subject headings:
Labor unions--Germany--Political activity--History.
Labor unions--Political activity--Germany--History.
Labor unions--Political activity--Great Britain--History
Labor unions--Political activity--Great Britain--History.
Labor unions--Political activity--United States--History
Labor unions--Political activity--United States--History.
Princeton subject headings:
Labor unions--Germany--Political activity--History.
Labor unions--Political activity--Great Britain--History.
Labor unions--Political activity--United States--History.