Columbia subject headings:
Harvard subject headings:
Labor unions--Portugal--Porto--History--20th century.
Porto (Portugal)--Social conditions--20th century.
Strikes and lockouts--Portugal--Porto--History--20th century.
Working class--Portugal--Porto--History--20th century.
Princeton subject headings:
Labor unions--Portugal--Porto--History--20th century.
Porto (Portugal)--Social conditions--20th century.
Strikes and lockouts--Portugal--Porto--History--20th century.
Working class--Portugal--Porto--History--20th century.