President Donald Trump’s plans to slap tariffs on steel and aluminum imports is a black day for the world and business, according to the biggest mining company.

BHP Billiton Ltd. and competitors could be hit should other economies follow the move by the U.S. toward a more protectionist and anti free-trade agenda, Chief Executive Officer Andrew Mackenzie said Tuesday at a business summit in Sydney. The U.S. tariffs are “a black day for the world and business,” he said.

“I am worried about this sentiment shift that people all around the world might suddenly say that free trade isn’t good for the world and that would be particularly bad for a trading company like BHP,” Mackenzie said during a panel on the economy. “We have to speak up loudly against these measures as being bad for America and bad for the world.”

BHP joins the chorus of global criticism from business and government that’s greeted Trump’s plans to impose tariffs of 25 percent on imported steel and 10 percent on aluminum. His surprise announcement Thursday roiled global financial markets amid mounting concern of an international trade war.

“Free trade is self-evidently the lifeblood of the global economy, and we expect it to flourish despite the regrettable developments in the U.S.,” Mackenzie said. Outside the U.S., “we observe buoyant economic conditions underpinned by the growth of free trade,” he said.

The move came after an inquiry sparked by U.S. metal producer complaints that they were hobbled by lower-cost output from China and other countries. Mackenzie said he would like to see the U.S. and China work more closely together despite ongoing conflict.

“I certainly see the tensions,” said Mackenzie. “I hope over time they can find a way of working together.”