US President Donald Trump has threatened further economic measures against the European Union over its plan to open a path for Canada to become the bloc’s first associate member, according to DW.

European Commission President Ursula von der Leyen announced the proposal during her annual speech at the European Parliament in Strasbourg. The arrangement would be a new form of relationship for the EU and would need to be created from scratch, the report said.

Speaking to reporters on Wednesday while travelling to an event in North Carolina, Trump said the proposal could constitute “a hostile act.” He said that, if he regarded it as hostile, he would impose “very serious tariffs” or stop trading with Europe on many goods. Trump also described the prospect of Canada joining the EU as “laughable.”

The proposal comes amid deteriorating relations between Washington and Ottawa during Trump’s second term. Canada was among the first countries affected by his tariff policy, and tensions intensified after trade talks between the two governments broke down last month.

Trump subsequently imposed further sanctions on Canada, while Canadian Prime Minister Mark Carney vowed to respond in kind, according to DW. The report does not provide details of the proposed EU-Canada arrangement or say that Canada has formally applied for associate membership.

US relations with Europe have also come under strain. Trump has pushed for US control of Greenland, an Arctic island that is part of the Kingdom of Denmark, while the EU was affected by his broad tariff measures imposed on countries around the world. Washington and Brussels later reached a trade agreement intended to reduce those tariffs, the report said.