Columbia subject headings:
Labor movement--Puerto Rico--Bibliography.
Labor movement--Puerto Rico--History--Sources--Bibliography.
Working class--Puerto Rico--Bibliography.
Working class--Puerto Rico--History--Sources--Bibliography.
Harvard subject headings:
Labor movement--Puerto Rico--Bibliography.
Labor unions--Puerto Rico--Bibliography.
Working class--Political activity--Puerto Rico--Bibliography.
Working class--Puerto Rico--Political activity--Bibliography.
Princeton subject headings:
Labor movement--Puerto Rico--Bibliography.
Labor unions--Puerto Rico--Bibliography.
Working class--Puerto Rico--Political activity--Bibliography.