Columbia subject headings:
Labor unions--Pennsylvania--History--20th century.
Pennsylvania--Emigration and immigration--History--20th century.
Pennsylvania--Social conditions.
Working class--Pennsylvania--History--20th century.
Harvard subject headings:
Labor unions--Pennsylvania--History--20th century.
Pennsylvania--Emigration and immigration--History--20th century.
Pennsylvania--Social conditions.
Working class--Pennsylvania--History--20th century.
Princeton subject headings:
Labor unions--Pennsylvania--History--20th century.
Pennsylvania--Emigration and immigration--History--20th century.
Pennsylvania--Social conditions.
Working class--Pennsylvania--History--20th century.