The anticipated letter is expected to detail fresh duties on imports from the EU, which remains Washington’s largest trading and investment partner.

Cars and tariff levels on agriculture have emerged as key sticking points between the European Union and the US as the two sides work toward a provisional trade agreement in the coming days, according to people familiar with the matter.

President Donald Trump on Saturday threatened to impose a 30% tariff on imports from Mexico and the European Union starting on Aug. 1.