The U.K. has “deep concern” about the U.S. plan to slap tariffs on steel and aluminum imports, and negotiated accords are better, Prime Minister Theresa May told President Donald Trump.

The two leaders spoke Sunday by telephone, with May saying “multilateral action was the only way to resolve the problem of global overcapacity in all parties’ interests,” according to a spokesman for the prime minister.

Trump’s vow that trade wars are good and are easy to win also drew a rebuke from one of May’s most senior ministers, who said the conflicts are bad and hard to win.

“I just think that the U.S. is not taking an advisable course in threatening a trade war,” U.K. Cabinet Office Minister David Lidington said Sunday on the BBC. “Trade wars don’t do anybody any good.”

The Trump administration could announce the levies of 25 percent on imported steel and 10 percent on aluminum as soon as this week. The plan rocked financial markets and led critics to say U.S. jobs were at risk and the plan might set off a global trade war.

Trump’s latest action is a particular embarrassment to the prime minister, who spent significant political capital in 2017 getting close to the president in the hope that she could secure a post-Brexit trade deal with the U.S.

Lidington said Britain’s experience over decades was that protectionism wasn’t the war to help domestic industries. “We tried in Britain in the 60s and 70s protecting our car industry from competition,” he said. “It actually didn’t work. It protected inefficiencies, we lost all our export markets because our competitors who were more competitive went out and gobbled those up from us.”

He expressed doubt that Trump’s proposal would go ahead. “There was a lot of concern recently about something comparable as regards aviation and the aircraft that were being produced in part by Bombardier, at Belfast in Northern Ireland and the American authorities at the end of the day struck that down,” he said.