China files World Trade Organization challenge to Trump’s latest tariff threat.

WASHINGTON » The Trump administration on Monday brought cases against China, the European Union, Canada, Mexico and Turkey at the World Trade Organization for retaliating against American tariffs on imported steel and aluminum.

The United States has imposed tariffs of 25 percent on steel and 10 percent on aluminum on the grounds that the imported metals pose a threat to U.S. national security. China, the EU, Canada, Mexico and Turkey have counterpunched with taxes on more than $24 billion worth of U.S. exports.

U.S. Trade Rep. Robert Lighthizer said their retaliation violates the rules of the Geneva-based WTO, which mediates trade disputes.

“Instead of working with us to address a common problem, some of our trading partners have elected to respond with retaliatory tariffs designed to punish American workers, farmers and companies,” Lighthizer said.

If the WTO agrees that the retaliatory duties violate its rules, it would assess the damage and calculate the tariffs that the United States would be entitled to impose in response — retaliation for the retaliation. But WTO proceedings can drag on for years.

In taxing imported steel and aluminum from some countries in March and others in June, President Donald Trump deployed a little-used weapon in American trade policy: Under the Trade Expansion Act of 1962, presidents are empowered to impose unlimited tariffs on imports that the Commerce Department asserts are threats to America’s national security.