Bloomberg reported that the tariffs are being broadly imposed, applying to imports from allies such as the EU, Canada and Mexico and to finished metal products. 

"Our nation requires steel and aluminum to be made in America, not in foreign lands we need to create in order to protect our country's future resurgence of U.S. manufacturing and production, the likes of which has not been seen for many decades," Trump said on Monday.

The action drew applause from the Steel Manufacturers Association (SMA), which said that Trump clearly understands that America’s steel industry is the backbone of its economy. 

“The steel industry in America faces serious threats from foreign actors that seek to destroy domestic production. China and other countries routinely violate trade laws and dump heavily subsidized steel products into the United States at the expense of American workers. By imposing a 25% tariff on steel imports, President Trump is leveling the playing field for American manufacturers and workers and helping America defeat direct threats to our jobs,” said SMA president Philip K. Bell. 

However, leaders in other parts of the world reacted angrily. 

The European Commission, for example, called the tariffs counterproductive.

“By imposing tariffs, the U.S. would be taxing its own citizens, raising costs for business and fueling inflation. Moreover, tariffs heighten economic uncertainty and disrupt the efficiency and integration of global markets,” it said in a statement.

European Commission President Ursula von der Leyen promised that the E.U would respond in kind. 

"Tariffs are taxes - bad for business, worse for consumers. Unjustified tariffs on the EU will not go unanswered— they will trigger firm and proportionate countermeasures," she said. 

Canadian Prime Minister Justin Trudeau also called the tariffs unjustified and promised a "firm and clear response."