President Donald Trump, who pledged to end the alleged “war on coal” and likes to surround himself with coal miners, may have just ended U.S. coal exports from the West Coast. “In trying to land a blow on the Canadian timber industry,” says Eric de Place, policy director of Seattle, Washington’s Sightline Institute, “Trump may have accidentally knocked out the Western coal industry.”

On Monday, at the urging of the U.S. timber industry, Trump imposed tariffs of up to 24 percent on imports of Canadian softwood lumber. The issue of Canadian lumber imports has been vexed for years, but this latest hardball from Trump—especially at a time when he is threatening to pull the United States out of NAFTA—hit a nerve with Canada. On Tuesday, Prime Minister Justin Trudeau promised to stand up for Canada’s lumber industry, warning, “You cannot thicken this border without hurting people on both sides of it.”

Today, British Columbia Premier Christy Clark dropped a bombshell tweet, saying, “It’s time to ban thermal coal from BC ports.” In a letter to Trudeau, she wrote:

For many years, a high volume of U.S. thermal coal has been shipped through BC on its way to Asia. It’s not good for the environment, but friends and trading partners cooperate. So we haven’t pressed the issue with the federal government that regulates the port.

Clearly, the United States is taking a different approach. So, I am writing you today to ban the shipment of thermal coal from BC ports.

Clark goes on to note the success of the Beyond Coal movement in shutting down coal terminals on the U.S. Pacific Coast:

As you may know, over the past five years, every proposed coal export facility on the West Coast of the United States has been rejected or withdrawn, typically as a result of ecological or environmental concerns. . . . Oregon, Washington, and California have all made significant commitments to eliminate the use of coal as a source of electricity for their citizens. In fact, in August 2016, Governor Jerry Brown of California signed Bill 1279 that banned the provision of any state transportation funding for new coal export terminals.

Due to the lack of U.S. terminals, Clark says, U.S. exports through Canada have been increasing. Last year, she says, 6.2 million tons of U.S. thermal coal moved through the Port of Vancouver, and the number was expected to increase in the future.

Or not. “In the context of how bad off [U.S. mines in the Powder River Basin] are,” says Sightline’s de Place, “this could be what brings them to their knees.” The closure of Canadian ports will be especially damaging to Cloud Peak Energy, which does most of the shipping out of Canada.

In provoking a trade war with our erstwhile friends and neighbors to the north, Donald Trump has started his own War on Coal.