Trump picks fight with Canada over dairy products and trade He called Canada's trade rules a "disgrace" last week.

 -- President Donald Trump tweeted Tuesday morning that the United States 'will not stand for' Canadian dairy trade policies that hurt American dairy farm exports, adding that the rules have "made business for our dairy farmers in Wisconsin and other border states very difficult."

Canada has made business for our dairy farmers in Wisconsin and other border states very difficult. We will not stand for this. Watch! — Donald J. Trump (@realDonaldTrump) April 25, 2017

It's the third time in the last week that Trump has bashed America's northern neighbor and close ally for its rules on imported dairy products.

"In Canada, what they've done to our dairy farm workers is a disgrace. It's a disgrace," Trump said in the Oval Office last week, as the President welcomed union leaders, steel workers and CEOs of steel companies for the signing of the memorandum ordering an investigation into steel dumping.

Trump made similar remarks in Wisconsin last Tuesday, calling the dairy trade relationship between the United States and Canada "very, very unfair."

"We're also going to stand up for our dairy farmers in Wisconsin," Trump told the crowd. "I've been reading about it and I've been talking about it for a long time and that demands, really, immediately, fair trade with all of our trading partners."

"That includes Canada, because, in Canada, some very unfair things have happened to our dairy farmers and others," Trump continued. "It's another typical one-sided deal against the United States and it's not going to be happening for long."

Several countries with high dairy product exports oppose Canada's current protectionist policies, which include high tariffs on imported milk and cheese products.

Trump based his 2016 presidential campaign on increasing the number of jobs in the United States by renegotiating trade pacts like the North American Free Trade Agreement (NAFTA) and withdrawing from the Trans-Pacific Partnership (TPP), both of which Canada has signed.

Halting business from moving overseas has been a key promise of Trump's early presidency.

The comments precede the upcoming renegotiation of NAFTA, expected this summer. The U.S. has been at odds with Canada over other imports, as well; one of the largest disputes has been about softwood lumber imports from Canada to the U.S. On Monday, Trump told media attending a reception that he would impose a 20 percent tariff on imports of the Canadian product.

Secretary of Commerce Wilbur Ross told reporters in today's White House briefing that even though Canada is a "good neighbor, that doesn't mean they don't have to play by the rules." He went on to say "there may be a small increase" in lumber prices because of the tariff.

Ross added that it's not a matter of "Trump messing with the Canadians," but rather, the White House believes "they violated legitimate practice."

The tariff would be "collected on a retroactive basis going back 90 days," Ross added.

ABC News' Katherine Faulders contributed to this report.