Donald Trump's decision to impose tariffs on steel and aluminum imports creates a lot of uncertainty, especially in Europe.
While Trump exempted neighbours Canada and Mexico, which together account for a quarter of US steel imports, the countries likely to suffer most are the EU, Brazil, South Korea and Japan.
The EU Council President put the issue on the agenda of the EU summit next week.
Donald Tusk's message from Finland: "Make trade, Mr. President, not war".
"Mr Trump has also said that real friends will be excluded from the proposed measures. I would like to stress today that the free world has survived the most difficult decades only thanks to the fact that Europeans and Americans have been real friends. So let us cherish this friendship, not challenge it".
At the European Parliament in Strasbourg, EU Trade Commissioner announced plans to challenge Trump's tariffs before the World Trade Organization.
"The security exemption that doies exist in the WTO but which is meant to be used for war times is misused. So, we are confident that we could win such a case in the WTO and we are reaching out two other friends and allies to see if we can make a joint approach to the WTO".