“Canada has made business for our dairy farmers in Wisconsin and other border states very difficult. We will not stand for this. Watch!” Trump tweeted Tuesday morning.

Trump has criticized Canada for its protections on prices for milk in the past, and Canada has a high tariff on imported dairy products. Trump has called the change in policy “a disgrace” and a “one-sided deal.” He vowed to defend U.S. dairy farmers affected by it during a visit to Wisconsin earlier this month.

“We’re also going to stand up for our dairy farmers,” Trump said in his speech. “Because in Canada some very unfair things have happened to our dairy farmers and others.”

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

On Monday, the Trump Administration said it would impose new tariffs averaging at 20% for Canadian lumber companies. Commerce Secretary Wilbur Ross said the new tariffs were imposed after a trade dispute between the two countries over dairy products.

“It’s been a bad week for U.S.-Canada trad relations,” Ross said.

“This is not our idea of a properly functioning Free Trade Agreement,” he added.

Canadian officials called the new tariff “an unfair and punitive duty,” and said “the accusations are baseless and unfounded.”

Trump has criticized the North American Free Trade Agreement between the U.S., Canada and Mexico, and has repeatedly threatened to pull the U.S. from NAFTA if he cannot get a better deal for the United States. However, Thomas Donohue, president and chief executive of the U.S. Chamber of Commerce, said the Trump Administration has a “constructive” approach to NAFTA, and is urging the President to amend the trade deal rather than leave it.