BRUSSELS (AP) — European Council President Donald Tusk says the European Union must prepare for the worst due to the policies of U.S. President Donald Trump, as a trade war looms between Washington and Brussels.

In a letter to EU leaders Wednesday, Tusk wrote that "trans-Atlantic relations are under immense pressure due to the policies of President Trump."

Tusk, who chairs a two-day summit of EU leaders in Brussels starting Thursday, said that "unfortunately, the divisions go beyond trade."

He wrote: "It is my belief that, while hoping for the best, we must be ready to prepare our Union for worst-case scenarios."

Earlier this month, Trump slapped tariffs on imports of European steel and aluminum. The EU responded with "rebalancing measures" that hit around 2.8 billion euros ($3.25 billion) worth of U.S. products.