Canada’s provincial premiers should cut red tape on trade at home and maintain solidarity with Prime Minister Justin Trudeau in the face of U.S. “protectionist attacks,” the head of a major business group says.

With premiers beginning a meeting Wednesday, Chamber of Commerce President Perrin Beatty is urging them to make it easier to do business and break down stubborn trade barriers between provinces that hurt growth.

“The competitiveness of Canadian businesses is eroding,” Beatty wrote in a letter to the incoming chairman of the premiers’ group, New Brunswick Premier Brian Gallant. “The issue has become even more urgent as a result of U.S. tax and regulatory reforms and of the attack on our trading relationship with our largest customer.”

Given the uncertainty over U.S. trade policy, trading within Canada is more important than ever, Beatty wrote. “Barriers to the free flow of goods and services between provinces are self-inflicted wounds that penalize consumers, make our businesses less competitive and undermine economic growth,” he said, adding too little has changed despite the adoption of an internal Canadian Free Trade Agreement that kicked in last year.

It’s a message that Trudeau himself echoed. “You can understand it’s kind of frustrating, not just for Canadians but for me, to see continued barriers to internal trade in Canada,” the prime minister told reporters Tuesday in Nova Scotia. To demonstrate the merits of trade, “we need to do a better job of doing it here in Canada.”