The Financial Times reports that the European Union has threatened to retaliate if US President Donald Trump places tariffs on European cars.

The European Commission reportedly sent a letter to the US threatening to hit $300 billion of American goods with tariffs.

The letter also said any auto tariffs would "damage further the reputation" of the US, according to the FT.

The European Union has reportedly threatened to retaliate against US President Donald Trump in the escalating trade conflict developing across the Atlantic.

According to a report in the Financial Times, a letter sent by the European Commission to the US Department of Commerce says the EU could hit $300 billion of US goods with tariffs if Trump follows through on his threats to place big taxes on European vehicles being imported in the US.

The EU's letter reportedly said the bloc had not yet decided on countermeasures to any new auto tariffs but said it was "likely" to apply them to "a significant volume of trade" in the event Trump imposed such tariffs.

Those measures would apply "across sectors of the US economy," the letter reportedly said. The US imported over $43 billion worth of vehicles for people transportation in 2017.

Along with the tariff threats, the European Commission is also believed to have warned Trump that his behavior could "result in yet another disregard of international law" by the US and said that any auto tariffs would "damage further the reputation" of the country.

Trump has sparked a global trade conflict by placing or threatening punitive tariffs on hundreds of billions of dollars' worth of goods from China, Mexico, Canada, and the European Union.

Trump recently turned his attention to the automotive sector, focusing on European manufacturers. "Based on the Tariffs and Trade Barriers long placed on the US and it great companies and workers by the European Union, if these Tariffs and Barriers are not soon broken down and removed, we will be placing a 20% Tariff on all of their cars coming into the US," Trump tweeted back in June. "Build them here!"

While he has threatened auto tariffs, Trump has not yet followed through on them.

He did, however, double down Sunday. "The European Union is possibly as bad as China, just smaller," he told Fox News in an interview, adding that it was "terrible what they do to us" and then mentioning the "car situation."

In this context, Trump presumably alluded to his belief that European carmakers were taking away business from American manufacturers.