U.S. President Donald Trump on Wednesday signed a proclamation to address the effects of copper imports, imposing universal 50 percent tariffs on imports of semi-finished copper products and copper-intensive derivative products, effective on Aug. 1.

The proclamation directs the U.S. secretary of commerce to establish a product "inclusion" process to add copper derivative products to these tariffs, and the president is authorizing the secretary of commerce to take steps under the Defense Production Act to support the domestic copper industry, the White House said in a fact sheet.

"By taking these actions, President Trump is leveling the playing field for U.S. copper businesses to support a strong domestic copper industry," the White House added.

Copper is essential to the manufacturing foundation on which U.S. national and economic security depend, and is a necessary input in a range of defense systems, including aircraft, ground vehicles, ships, submarines, missiles and ammunition, according to the fact sheet.

U.S. copper futures on Comex plunged 20 percent after the announcement, Bloomberg reported. Until Wednesday afternoon, U.S. copper prices had been trading around 28 percent above benchmark copper futures on the London Metal Exchange, as traders anticipated the tariff would be applied to all refined metal imports.

The decision is the latest surprise from Trump to upend the copper market, Bloomberg said in its report. When the president first flagged the likelihood of tariffs early this year, he triggered a surge in U.S. copper prices relative to the rest of the world and set off a race to ship copper to the United States to beat the tariffs, delivering substantial profits to some of the world's biggest metals traders.