Donald Trump announced Monday that the United States will impose a 20 percent tariff on all softwood lumber imported from Canada in order to level the playing field for American lumber companies.

“We love Canada, but they have been very good at taking advantage of the United States through NAFTA,” Trump told a group of reporters in the Roosevelt Room. “We are putting a 20 percent tax on lumber coming into the United States from Canada.”

“Canada has treated us very unfairly.”

A senior administration noted that the tariff will be applied retroactively. When asked what that tax will mean for lumber production, Trump said, “It means we’re going to start doing lumber in our country.”

“We’re going to actually do our own lumber,” he said. “We will have access to great amounts of lumber.”

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The decision to tax Canadian lumber comes as the countries prepare to negotiate the North American Free Trade Agreement, which Trump has criticized repeatedly.

On Twitter Tuesday morning, Trump implied that a tax on Canadian dairy products could be next.