“If the E.U. wants to further increase their already massive tariffs and barriers on U.S. companies doing business there, we will simply apply a Tax on their Cars which freely pour into the U.S.” he wrote. “They make it impossible for our cars (and more) to sell there. Big trade imbalance!”

The President’s comments came just days after several European leaders reacted sharply to the President’s tariff announcement.

“We will not sit idly while our industry is hit with unfair measures that put thousands of European jobs at risk,” European Commission President Jean-Claude Juncker said in a statement.

“Instead of providing a solution, this move can only aggravate matters,” his statement said.

German Foreign Minister Sigmar Gabriel said, “the EU must respond decisively to US punitive tariffs, which endanger thousands of jobs in Europe. There should be no doubt about that in Washington.”

Canada, meanwhile, said that any trade restrictions on Canadian steel and aluminum would be “absolutely unacceptable.”

“Should restrictions be imposed on Canadian steel and aluminum products, Canada will take responsive measures to defend its trade interests and workers,” Canadian Foreign Minister Chrystia Freeland said in a statement.

The details of Trump’s policy — which is not yet official — are expected to be announced next week.