US Trade Representative Robert Lighthizer said in a statement that the retaliatory tariffs on up to a combined US$28.5 billion worth of US exports are illegal under WTO rules.

“These tariffs appear to breach each WTO member’s commitments under the WTO Agreement,” Lighthizer said. “The United States will take all necessary actions to protect our interests, and we urge our trading partners to work constructively with us on the problems created by massive and persistent excess capacity in the steel and aluminium sectors.”

Lighthizer’s office has maintained that the steel and aluminium tariffs are acceptable under WTO rules because they were imposed on the grounds of a national security exception.

Lighthizer said last month that retaliation had no legal basis because the EU and other trading partners were making false assertions that the US steel and aluminium tariffs are illegal “safeguard” actions intended to protect U.S. producers.