The Canadian National Policy was a tariff law created in the late 1800s designed to help Canadian manufacturing become a strong economic factor. Before the adoption of the National Policy, factories in Canada were rare, and the bulk of manufactured products were imports. Due to high export tariffs enforced by the U.S., widespread Canadian manufacture was not yet economically viable. The National Policy raised import taxes to encourage local manufacture.
The National Policy act was passed, so it cannot be said to have been unconstitutional at the time. However, changing laws and rulings by courts, as well as the opposition of the Progressive Party, caused it to be revoked in pieces over the next fifty years, finally becoming fully defunct in 1988. Current interpretations of the Canadian Constitution prevent a return of this sort of protectionist policies, but some recent opinions advocate a similar plan to increase Canada's economic standing.