Trump has said he wants to reduce his country's longstanding trade deficit with the EU, which occurs when a country imports more than it exports. He blames the deficit on policies that he says are unfair to American companies.
On Friday, Trump said the EU had been "very difficult to deal with" and that the bloc had been formed "for the primary purpose of taking advantage" of the United States on trade.
"Our discussions with them are going nowhere! Therefore, I am recommending a straight 50% Tariff on the European Union, starting on June 1, 2025," he added.
Trump said there would be no tariff charged if the product was "built or manufactured in the United States".
Trump has repeatedly complained about the EU's car exports, particularly from Germany, to the US, with fewer vehicles being shipped the other way.
The boss of carmaker Volvo said in response to Trump's threat that customers would have to pay a large part of the cost increases resulting from tariffs.
Hakan Samuelsson told Reuters that a 50% tariff would limit the ability of the company to sell its Belgium-made EX30 electric vehicle across the Atlantic.
But he said he believed there would be a deal soon. "It could not be in the interest of Europe or the US to shut down trade between them," he said.
While some higher tariffs have been paused by Trump, foreign-made cars have faced a 25% levy since April.
Trump's warning to Apple comes after the tech giant said it was shifting production of most of its iPhones and other devices destined to be sold in the US away from China.
Apple chief executive Tim Cook said earlier this month that the majority of the iPhones bound for the US market in the coming months are to be made in India, while Vietnam will be a major production hub for items like iPads and Apple Watches.