The U.S. administration has not extended the tariff exemptions on imports of steel and aluminum for its major Western trading partners on Thursday. The World Trade Organization (WTO) can allow those countries to retaliate against the tariffs within its framework, up to the amount of their respective estimated losses.
However, the WTO would have to find that the Trump administration was wrong to quote national security reasons to impose the tariffs in the first place. According to figures published by the Peterson Institute for International Economics (PIEE)
, Canada could retaliate by imposing tariffs worth some $3.2 billion.