President Trump on Friday signed a proclamation expanding tariffs on steel and aluminum imports from some countries. 

The proclamation boosts tariffs on derivative steel products by another 25 percent and increases tariffs on derivative aluminum products by another 10 percent. The increase expands on existing tariffs that had sat at 25 percent on steel and 10 percent on aluminum. 

Trump exempted several countries from the increase: Argentina, Australia, Brazil, Canada, Mexico and South Korea are exempt from the additional tariffs on steel products, and Argentina, Australia, Canada and Mexico are exempt from the added tariffs on aluminum goods.

The president has relied on tariffs to help strengthen U.S. production, an issue he says impacts national security.

Trump said in the proclamation that foreign producers have boosted the shipments of derivative goods in order to circumvent the existing duties on steel and aluminum.

“[I]mports of these derivative articles threaten to undermine the actions taken to address the risk to the national security of the United States,” Trump said in the proclamation. “[D]omestic production capacity to produce aluminum articles and steel articles for national defense and critical infrastructure is essential to United States national security.

“I have concluded that it is necessary and appropriate in light of our national security interests to adjust the tariffs imposed by previous proclamations to apply to the derivatives of aluminum articles and steel articles,” he added. “This action is necessary and appropriate to address circumvention that is undermining the effectiveness of the adjustment of imports.” 

The tariff hike will take effect on Feb. 8.

Trump has maintained his penchant for imposing tariffs throughout his administration, seeing the duties as effective ways to protect U.S. manufacturers as well as tools to pressure foreign nations in negotiations.