Columbia subject headings:
Catholic labor unions--Germany--History--20th century.
Kopp, Georg, 1837-1914.
Labor--Religious aspects--Christianity--Germany--History--20th century.
Harvard subject headings:
Catholic labor unions--Germany--History--20th century.
Church and social problems--Germany--Catholic Church--History.
Kopp, Georg, 1837-1914
Labor unions--Germany--History
Labor--Religious aspects--Christianity--Germany--History--20th century.
Social movements--Germany--History.
Princeton subject headings:
Catholic labor unions--Germany--History--20th century.
Kopp, Georg, 1837-1914.
Labor--Religious aspects--Christianity--Germany--History--20th century.