President Trump signed a controversial order implementing heavy tariffs on imported steel and aluminum Thursday, calling the action “a matter of necessity for our security” and saying it would help to revitalize fading American industry.

“Our industries have been targeted for years and years—decades, in fact—by unfair foreign trade practices leading to shuttered plants and mills, the laying off of millions of workers and the decimation of entire communities,” Trump said. “That’s going to stop.”