Columbia subject headings:
Harvard subject headings:
Labor movement--Mexico.
Mexico--Politics and government--1910-1946.
Petroleum workers--Labor unions--Mexico.
Railroads--Employees--Labor unions--Mexico.
Princeton subject headings:
Labor movement--Mexico.
Labor unions--Mexico--History.
Mexico--Politics and government--1910-1946.
Petroleum workers--Labor unions--Mexico.
Railroads--Employees--Labor unions--Mexico.