In the wake of the U.S. doubling its tariffs on steel and aluminum, Prime Minister Mark Carney has called the new tariffs “unjustified” and pledged to respond — but what that response might look like isn’t clear yet.

US President Donald Trump’s order to double tariffs on steel and aluminum imports from 25% to 50% has come into effect. The move has been well-received by the American steel industry, but critics warn that it could have detrimental impacts on steel producers outside of the US and relations with trading partners.