On March 8, 2018, President Trump exercised "his authority to impose a 25 percent tariff on steel imports and a 10 percent tariff on aluminum imports" under Section 232 of the Trade Expansion Act of 1962. On April 30, 2018, the White House announced that it would suspend application of the Section 232 tariffs to Canada, Mexico, and the European Union ("EU") and its member countries until June 1, 2018. In that statement, the White House indicated that negotiations would remain "focused on quotas that will restrain imports, prevent transshipment, and protect the national security."

On May 31, 2018, however, the President announced that the tariffs would no longer be suspended for Canada, Mexico and the EU and would go into effect on June 1, 2018. The President noted that the Administration would continue discussions with these countries on this and related matters. He also announced that the Administration remained open to discussions with other countries on the tariffs as well.

Mexico, Canada and the EU responded immediately. Mexico’s Secretary of Economy, Ildefonso Guajardo, stated that, "Mexico will impose measures equivalent to various products such as flat steel, lamps, legs and pork shoulders, sausages and food preparations, apples, grapes, blueberries, various cheeses, among others, up to a comparable amount."

Canada’s Prime Minister, Justin Trudeau, announced that Canada would immediately take retaliatory measures against the United States. Canada plans to impose surtaxes and other retaliatory measures on steel and aluminum imports and other imports from the United States, with some imports being subject to a 25 % surtax and others being subject to a 10 % surtax. The surtaxes will go into effect on June 1, 2018. Canada intends to pursue a dispute settlement case under NAFTA against the United States and will work with the EU and other countries to challenge the new tariffs in the WTO.

Additionally, the EU confirmed that it will impose retaliatory tariffs on U.S. goods, as previously announced. On May 16, 2018, the European Commission (“EC”) had announced it would take retaliatory measures on certain goods originating in the United States. In that announcement, the EC stated that it will apply the additional duties in two stages. In the first stage, the EU will impose an additional duty of 25% on a number of products. In the second stage, it will impose an increase of 10%, 25%, 35%, or 50% on certain other products. The first stage of the measures will become effective on June 20, 2018, while the second stage will become effective on March 23, 2021 (or earlier if the World Trade Organization rules against the Section 232 tariffs).

The EC’s President, Jean-Claude Juncker, stated that the EU will also initiate a dispute settlement case against the United States in the WTO, asserting that the U.S. tariffs "are primarily intended to protect U.S. industry from import competition,” which is “at odds with WTO rules."

Another close ally of the United States, Japan, has not been granted a temporary exemption from the U.S. tariffs. At an April meeting between Prime Minister Shinzo Abe and President Donald Trump, the two discussed a possible exemption from the tariffs. The discussions did not yield concrete results. Since that meeting, in a filing at the World Trade Organization, Japan has indicated that it too will institute retaliatory tariffs. Unlike the European Union, Japan has not specified how they might retaliate against U.S. exports; Japan indicated, however, that it could impose retaliatory tariffs of more than $400 million of goods.

Although the EU, Japan, Canada and Mexico have long enjoyed cordial trade relations with the United States, it is not clear whether the countries will be able to avoid implementation of additional tariffs, at least in the short term. Indeed, on May 23, 2018, the White House issued a statement indicating that the President met with Secretary of Commerce Wilbur Ross to "consider initiating a Section 232 investigation into imports of automobiles, including trucks, and automotive parts to determine their effects on America’s national security." If tariffs are imposed on imports of these products into the United States, it could have a significant impact on Japan, the EU, Canada and Mexico.