President Donald Trump threatened additional tariffs on the European Union after European Commission President Ursula von der Leyen proposed closer ties with Canada.

Speaking in Charlotte, North Carolina, Trump said the level of any new tariffs would depend on what he described as the EU’s intentions.

He warned that tariffs could become “very heavy” and potentially affect trade in certain areas.

Trump also criticized the idea of Canada becoming an associate EU member, calling the proposal “laughable” and describing Canada as a poor trade partner, CBS News has reported.

The comments add another point of tension as Canada seeks closer economic ties with Europe amid ongoing trade disputes with the United States.