For the second time this week, U.S. President Donald Trump has given Canada a verbal lashing over what he says are unfair trade practices that are putting Americans out of work.

Trump made his, apparently unplanned, remarks from the Oval Office before signing a presidential memorandum directing his Department of Commerce to investigate the national security implications of importing foreign-made steel.

"I wasn't going to do this," Trump said. "I was in Wisconsin the other day, and I want to end and add by saying that Canada what they've done to our dairy farm workers is a disgrace. It's a disgrace."

Trump then moved on to criticizing Canada for using NAFTA to take advantage of the U.S. when it comes to the trade in lumber and energy between the two countries.

U.S. president calls Canada's dairy trade 'a disgrace' and 'a disaster' 1:24

"The fact is NAFTA, whether it's Mexico or Canada, is a disaster for our country. It's a disaster. It's a trading disaster. And we'll be reporting back some time over the next two weeks as to NAFTA and what we are going to do about it," Trump said.

"What happened to our dairy farmers in Wisconsin and New York state, we're not going to let it happen, We can't let Canada or anybody else take advantage and do what they did to our workers and to our farmers. And again I want to also just mention: included in there is lumber, timber and energy.

"So, we're going to have to get to the negotiating table with Canada very, very quickly."

Speaking in Wisconsin on Tuesday, Trump criticized some recent moves by the Canadian dairy industry.

Trump appeared to be taking issue with Canadian dairy producer's decision to lower the price of dairy ingredients to make Canadian products more affordable, which drew business away from producers in Wisconsin and New York state.

The Dairy Farmers of Canada also updated their brand strategy to help consumers spot American ingredients on grocery shelves.

Softwood lumber investigation underway

The comments come after an April 13 ruling by a NAFTA panel ordering the U.S. to reconsider duties levied against Canadian paper mills that produce supercalendered paper, which is used in the production of magazines, brochures and other products.

On Wednesday, the Department of Commerce also gave notification that it would postpone a planned decision on whether or not to impose anti-dumping duties on some Canadian softwood lumber products, which it has been investigating since December of last year.

The department was due to release the results of that investigation on May 4, but it asked for an extension in order to have "sufficient time to obtain and review all relevant information from the parties to this proceeding," according to the U.S. Federal Register, a daily journal of the U.S. government.

Defending Canada

Minister of Foreign Affairs Chrystia Freeland issued a statement saying that the federal government supports "rules-based" trade and will continue to defend Canada's interests.

"With respect to softwood lumber, our producers and workers have never been found in the wrong," she said. "The softwood industry supports thousands of jobs in both countries and has downstream benefits in communities across the continent.

"The United States needs Canadian lumber. A protracted dispute will only drive up the cost of wood and homes for U.S. consumers."

Freeland said that Canada buys more from the U.S. than any other country, including the European Union, Mexico, China and Japan and that nine million jobs in the U.S. depend on trade and investment with Canada.

"Any increase of trade barriers between our countries would significantly impact jobs in the United States, as well as in Canada."