The introduction of U.S. tariffs on European Union automobiles and car parts could affect $300 billion in trade and damage nearly all of the bloc’s 28 member states, according to an EU report.

Duties of 25 percent “could be expected roughly to reduce U.S. imports of car and car parts in half,” the European Commission wrote in a memo obtained by Bloomberg. “An introduction of U.S. tariffs would be met with equivalent penalties imposed by affected trading partners.”

President Donald Trump said Friday on Twitter that he would impose a 20 percent levy on all cars imported from the EU unless the bloc removes import duties and trade barriers. This comes on the same day that the EU triggered tariffs on 2.8 billion euros ($3.3 billion) of American products in response to U.S. duties on its steel and aluminum exports that were justified on national security grounds.

EU and U.S. auto-related trade accounts for some 10 percent of total commerce between the two regions, according to the European Automobile Manufacturers’ Association. The U.S. is the number one destination of EU car exports both in terms of volume -- making up around a fifth of all exports -- and revenue with just under a third of total export value.