The Teamsters union, one of the largest labor groups in North America, is backing its Canadian members in a push to end the steel and aluminum tariffs imposed by President Trump.

"The implementation of these tariffs and the inevitable retaliatory tariffs by Canada will immediately harm workers in both nations," the Teamsters said in a statement, echoing the concerns of corporate executives and economists who fear the White House's protectionist policies will ignite a trade war.

The duties of 25 percent on steel imports and 10 percent on aluminum were imposed on some of the closest U.S. allies – Mexico, Canada, and Europe – in late May, spurring prompt retaliation. When Canadian Prime Minister Justin Trudeau told reporters after the Group of 7 gathering that his country, while polite, wouldn't be pushed around, members of the Trump administration took it a personal insult and accused him of backstabbing.