Columbia subject headings:
Canada--Commerce--United States.
Free trade--United States.
Tariff--Canada.
Tariff--United States.
United States--Commerce--Canada.
Harvard subject headings:
Canada. Treaties, etc. 1988 January 2.
Duty-free importation--Canada.
Duty-free importation--United States.
Tariff--Canada
Tariff--United States.
Princeton subject headings:
Canada--Commerce--United States.
Free trade--Canada.
Free trade--United States.
Tariff--Canada.
Tariff--United States.
United States--Commerce--Canada.