Canada filed a case against the U.S. at the World Trade Organization (WTO) on Friday, marking the latest effort by a key U.S. ally to put pressure on the Trump administration to remove stiff tariffs on steel and aluminum imports.

Canada joins the European Union (EU) in dragging a mounting trade dispute with the U.S. to the WTO, which regulates international trade.

Canadian Foreign Minister Chrystia Freeland decried what she called the Trump administration's "illegal tariffs" and accused the U.S. of undermining "the integrity of the global trading system."

"On top of the retaliatory measures announced yesterday, the Government of Canada today requested WTO consultations with the United States regarding its imposition of punitive tariffs on imports of steel and aluminium from Canada, and more generally, on the United States’ improper use of national security pretexts for protectionist purposes," Freeland said in a statement.

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The decision came a day after the Trump administration announced it would impose 25 percent tariffs on steel imports and 10 percent tariffs on aluminum imports from the EU, Canada and Mexico, putting an end to the group's temporary exemptions.

The EU, Canada and Mexico have already threatened retaliatory tariffs on U.S. goods, ranging from blue jeans to yogurt.

The U.S. has argued that the steel and aluminum tariffs are necessary to protect national security. The EU, Mexico and Canada have rebuffed that claim, arguing that they do not pose a threat to the U.S. and that American defense projects rely on their steel and aluminum exports.

Freeland on Friday called the Trump administration's national security argument a "false pretext" for taking "protectionist actions."

"It is entirely inappropriate to view any trade with Canada as a national security threat to the United States," she said.