"In Canada, some very unfair things have happened to our dairy farmers, and others", said Trump, in an address to the American dairy industry. "Nearly one year ago, we, along with other state and USA dairy officials, warned our federal partners - and Canadian industry and government representatives at all levels - that protectionist regulations would harm USA dairy producers".
He also signalled he wants to do more than simply tweak NAFTA, saying he is looking for "very big changes" to the trilateral pact that includes Mexico, or else he will scrap it once and for all.
Estimates of how much of Canada's softwood lumber is shipped to the US are as high as 70 per cent, but the Trudeau government has placed a priority on finding new trade markets in Asia - especially China - for a variety of goods and services.
New Zealand Trade Minister Todd McClay told Reuters in an email his government was assessing the "WTO-consistency" of Canada's dairy industry policy, and had raised concern with the Canadian government.
USA farmers have claimed they are losing up the US$150 million per year because of heavy import tariffs on ultra-filtered milk used to produce cheese.
A spokeswoman for Canada's dairy industry said Tuesday night there has not been any new taxes on dairy imports. Trump promised to work with Wisconsin's congressional delegation to get a solution after the governors of Wisconsin and NY urged him to take action. The U.S. exported $98 million worth of milk protein substances, including diafiltered milk, to Canada in 2016. "We have actually allowed more imports of dairy products into our country as a percentage (of GDP) than they have in theirs", he added.
The Dairy Farmers of Canada, which has previously denounced the complaints as "falsehoods and half-truths", said Tuesday it was confident the federal government would continue to defend the dairy industry.
Earlier this week, in Kenosha, Mr. Trump had promised to stand up for dairy farmers, though he didn't explain the issue, which, according to the Milwaukee Journal Sentinel, is likely a change in Canadian dairy pricing policies that undercut about 75 Wisconsin dairy farmers earlier this month.
Trudeau said he wants to have a fact-based conversation with the Americans, noting the US - like other countries - subsidizes its dairy and agriculture industries to the tune of hundreds of millions, if not billions, of dollars.More news: Fatal terror attack: Champs-Elysees in Paris
Kevin Ellis, CEO of Cayuga Milk Ingredients, said previous year that the Cayuga County company could lose $30 million in sales if Canada follows through with the trade policies.
The US dairy industry - particularly in Wisconsin, where some dairy farmers have already felt an economic impact - has slammed the Canadian practices as unfair and called on the Trump administration to take action.
"I wasn't going to do this", he said, but referring to his trip to Wisconsin this week, Mr. Trump said that what Canada had done to USA dairy farm workers was a "disgrace". "I think it's going to work out just fine".
"Different countries have different approaches, and we're going to engage in a thoughtful, fact-based conversation on how to move forward in a way that both protects our consumers and our agricultural producers", he said.
"We're going to have to get to the negotiating table with Canada very, very quickly", he added. Commerce Secretary Wilbur Ross has blamed the Senate for delaying the confirmation of Trump's USA trade representative.
"The whole thing is ridiculous".
Trump today included the lumber, timber and energy sectors in a list of what he said were problematic areas of trade with Canada, but did not give details.
Francois Dumontier, a spokesman for Les Producteurs de lait du Quebec, said imports of US milk products have increased since 1993 and now account for three-quarters of milk products in Canada.
Currently, American farmers are sending their ultra-filtered milk north of the border without being subject to tariffs, due to NAFTA which was approved in 1994.