Trump's tariffs face biggest test yet in U.S. Supreme Court

U.S. President Donald Trump's tariff regime faces its biggest legal test yet this week.

The U.S. Supreme Court will hear arguments Wednesday on Trump's unprecedented use of an emergency powers law to slap broad-based tariffs on imports from Canada and other major trading partners.

On social media Trump has called it “THE MOST IMPORTANT CASE EVER" and repeatedly claimed that the Ontario government's anti-tariff ad campaign featuring an address by the late Ronald Reagan was an attempt to interfere with the case.

Many billions of dollars are at stake. If the administration loses in the Supreme Court, it may have to return tariffs paid by importers since the spring and will forgo a source of revenue that Trump has claimed is making America rich again. 

Elizabeth Wydra, president of the Constitutional Accountability Center, a legal advocacy nonprofit in Washington, D.C., says the stakes are also high for the functioning of U.S. democracy and for the Supreme Court. 

“They have so far in this second Trump administration been very much acquiescent in Trump's power grabs," Wydra said in an interview with CBC News. "From a separation-of-powers, constitutional standpoint, the question is huge.”

Under the U.S. Constitution, only Congress has the power to tax or tariff, unless it passes a law that gives the president that authority. 

Trump used a 1977 law called the International Emergency Economic Powers Act (IEEPA) to levy broad-based tariffs over a pair of what he declared to be national emergencies: the cross-border trafficking of fentanyl (for tariffs on imports from Canada, Mexico and China) and the deep trade deficits the U.S. has with dozens of countries around the world (what Trump called his “Liberation Day” tariffs).

Whether IEEPA gives the president the legal authority to impose tariffs in this way and for those reasons is the fundamental issue before the court. 

The case does not test the long-established power of a president to impose tariffs sector by sector, as Trump has done with imports of steel, aluminum and automobiles, to protect specific U.S. industries. 

More than 40 organizations, individuals and interest groups have submitted "friends of the court" briefs ahead of Wednesday's hearing in an effort to sway the justices.

Nearly all of those submissions, also known as amicus briefs, urge the court to rule that Trump's use of IEEPA is illegal.

The list of those who've submitted legal briefs opposing the tariffs crosses a wide range of ideology, geography and profession, including some high-profile names:

There are also friend of the court submissions from: