Columbia subject headings:
Customs unions--Law and legislation--Canada.
Customs unions--Law and legislation--United States.
Free trade.
Tariff--Canada.
Tariff--United States.
Harvard subject headings:
Customs unions--Law and legislation--Canada.
Customs unions--Law and legislation--United States.
Free trade--Canada
Free trade--United States
Free trade.
Tariff--Canada
Tariff--Law and legislation--Canada.
Tariff--Law and legislation--United States.
Tariff--United States.
Princeton subject headings:
Canada. Treaties, etc. 1988 Jan. 2.
Free trade--Canada.
Free trade--United States.
Tariff--Law and legislation--Canada.
Tariff--Law and legislation--United States.