US President Donald Trump warned on Wednesday that he could regard any possible admission of Canada as an associate member of the European Union as a ‘hostile act’.

He threatened to respond with new tariffs on European products, News.ro reports.

Trump made the remarks to journalists in Charlotte, North Carolina. He said Washington’s response would depend on the intentions of European leaders.

If he considered the initiative hostile, the US could impose very severe tariffs or halt trade with Europe in many products.

The US leader called the idea ridiculous and criticised Canada as a trading partner. However, he did not specify which tariffs he had in mind or how he would determine whether the move was hostile.

The reaction came several hours after Ursula von der Leyen delivered her annual State of the Union address in Strasbourg, in the presence of Canadian Prime Minister Mark Carney.

The President of the European Commission proposed there that the EU open the way for Canada to become its first associate member. The relationship would go beyond the current free trade agreement, CETA, through an ‘Alliance for the Future’.

The cooperation would include manufacturing, technology, defence, artificial intelligence and the Arctic.

The proposed status has not yet been defined. The EU treaties do not provide for an associate membership category, von der Leyen did not detail the associated rights and obligations, and any move would require the support of the member states.

Several European capitals were reportedly caught off guard by the announcement. Brussels has not yet said whether it will pursue the proposal following Trump’s threat.

In Ottawa, Carney’s cabinet welcomed the prospect of closer ties with the EU, without explicitly backing associate membership. Jonathan Wilkinson, Canada’s designated ambassador to the EU, said that his country had not yet reached that point and that the priority was to secure concrete results.

The dispute comes against the backdrop of trade tensions between Washington and Ottawa. Canada is trying to reduce its dependence on the US market, where approximately 70% of its exports end up.

Also on Wednesday, Trump signed a memorandum excluding Canadian products from federal government procurement, in response to the Ottawa government’s ‘Buy Canadian’ policy.

Any new tariffs on the EU would put last year’s trade agreement between Washington and Brussels to the test; the deal caps tariffs at 15% on most European exports to the US.