US President Donald Trump on Saturday threatened to tax European cars if the European Union retaliates against his steep tariffs on aluminum and steel, The Hill reported.

Trump suggested in his tweet that the U.S. would not impose the aluminum and steel tariffs on the E.U. if they dropped their tariffs. 

"The European Union, wonderful countries who treat the U.S. very badly on trade, are complaining about the tariffs on Steel & Aluminum. If they drop their horrific barriers & tariffs on U.S. products going in, we will likewise drop ours. Big Deficit. If not, we Tax Cars etc. FAIR!" Trump tweeted.

Earlier this week, Trump officially announced tariffs of 25 percent on steel and 10 percent on aluminum, despite major opposition from his own party.

The EU threatened an "arsenal" of retaliatory measures when the tariffs were first proposed, including imposing import tariffs on products made in red districts.