U.S. refiners have become more reliant on heavy crude from Canada. Tariffs on Canadian crude oil imports could lead to higher gasoline prices for U.S. drivers.

The 10 percent tariff the president said he might impose in March could cause U.S. refineries to cut production and lead to higher prices.

The United States' promise to slap tariffs on Canada has plunged the country in to a state of economic uncertainty.