President Trump on Saturday initiated an investigation into whether imports of lumber threaten America’s national security, a step that is likely to further inflame relations with Canada, the largest exporter of wood to the United States.

The president directed his commerce secretary, Howard Lutnick, to carry out the investigation. The results of the inquiry could allow the president to apply tariffs to lumber imports. A White House official declined to say how long the inquiry would take.

An executive memorandum signed by Mr. Trump ordered the investigation and was accompanied by another document that White House officials said would expand the volume of lumber offered for sale each year, increasing supply and helping to ensure that timber prices do not rise.

The trade inquiry is likely to further anger Canada. Some of its citizens have called for boycotts of American products over Mr. Trump’s plans to impose tariffs on all Canadian imports beginning on Tuesday. The president, who also plans to hit Mexico with similar tariffs, says the levies are punishment for failure to stem the flow of drugs and migrants into the United States.

Many Canadians have contested Mr. Trump’s assertion that fentanyl is flowing from its country into the United States.

Canada and the United States have sparred over protections in the lumber industry for decades. The countries have protected their own industries with tariffs and other trade measures, and argued about the legitimacy of those measures in disputes both under the North American Free Trade Agreement and at the World Trade Organization.