NEW YORK— President Trump’s new tariffs on imported steel and aluminum took effect at midnight Wednesday, doubling the previous 25% duties to a staggering 50%. The move, aimed at shielding domestic producers, is expected to ripple across industries—from automotive and construction to grocery shelves—raising costs for manufacturers and consumers alike.

Trump says the higher tariffs are vital to defending U.S. industries and national security from a flood of cheap foreign metals, especially from China. He first unveiled the measure during a speech to steelworkers in Pennsylvania, touting it as a boost for U.S. steel and a planned partnership with Japan’s Nippon Steel.

The U.K. is the only exception: British metals remain subject to the original 25% tariff under a recent U.S.-U.K. trade agreement. That rate could drop to zero if the deal is finalized by July 9.

Steel prices in the U.S. have already surged 16% since January, far outpacing prices in Europe and China. And with retaliatory actions looming, global trade tensions may soon escalate. Mexico has called the tariffs “unfair and unsustainable” and is sending officials to Washington this week to seek exemption. The European Union, meanwhile, is preparing its countermeasures if negotiations fail by mid-July.