China, the European Union, Russia and Norway joined “several other” countries in asking the World Trade Organization to investigate the Trump administration’s decision to impose tariffs on metal imports, creating a new front in a trade war that has shaken global markets.

“We believe that the U.S.’s additional duty on steel and aluminum is in violation of the WTO rules,” Norway’s Foreign Minister Ine Eriksen Soreide said in a Thursday statement. Norway and the other nations “have therefore chosen to request the WTO to establish a dispute resolution panel to get an independent assessment of the matter,” she wrote.

The U.S. administration said the tariffs -- 25 per cent on steel imports and 10 per cent on aluminum -- are allowed under the WTO’s national security exemption, which permits governments to take “any action which it considers necessary for the protection of its essential security interests.” This has drawn the ire of affected countries, many of which are close American allies, such as the EU and Canada.

A spokeswoman for the office of the U.S. Trade Representative didn’t immediately respond to a request for comment; a WTO spokesman declined to comment on the matter.

The dispute puts the Geneva-based trade organization in a difficult position: If it rules in support of the U.S. it could encourage other members to enact protectionist measures under the guise of national security; If it rules against the U.S. it could draw further ire from the largest economy in the world.

The “worst outcome” for the WTO is if the dispute settlement system “decided that it was in a position to judge whether something was or was not in the national security interests of the U.S. or any other member,” Deputy U.S. Trade Representative Dennis Shea said in an October speech in Washington.

The requests will be considered at the next meeting of the WTO dispute settlement body, which is scheduled for Oct. 29.