President Trump warned on Thursday that he would impose higher tariffs on the European Union and Canada if they join forces against the U.S., as the trade war with these allies escalates.

“If the European Union works with Canada in order to do economic harm to the USA, large scale Tariffs, far larger than currently planned, will be placed on them both in order to protect the best friend that each of those two countries has ever had!” Trump wrote on Truth Social early Thursday morning.

The threat emerged just one day after Trump announced a 25 percent tariff on foreign-made vehicle imports—a measure expected to hit countries like Germany particularly hard.

European automakers criticized the move, arguing that it would damage U.S. manufacturing while further impacting nations already affected by Trump’s steel and aluminum tariffs on trading partners, The Hill noted.

The president also hinted at reciprocal tariffs set to take effect on April 2—dubbed “liberation day” by him—that would impose the same tariffs trading partners levy on the U.S.

Earlier this month, Trump announced broad tariffs on Canadian and Mexican imports and a one-month delay for auto parts covered under the U.S.-Mexico-Canada trade agreement, which is set to expire next week.