By Timothy Meyer

October 29, 2025

On October 25, 2025, U.S. President Donald Trump announced a new 10% tariff on Canadian imports, ostensibly in response to Ontario’s decision to run an ad featuring a speech by former President Ronald Reagan decrying tariffs.

The threat of new and additional tariffs on Canadian imports into the U.S. underscores the stakes for Canada in a U.S. Supreme Court case—known as Learning Resources v. Trump—that will be argued on November 5th. Since returning to the White House in January, Trump has imposed a sweeping array of tariffs on nearly all U.S. trading partners. While he has invoked familiar legal authorities from his first term, such as Section 232 of the Trade Expansion Act of 1962, his most extreme actions have rested on the International Emergency Economic Powers Act (IEEPA).

Historically, presidents have used IEEPA—which authorizes the president to act after he has declared a national emergency with respect to an unusual and extraordinary threat to U.S. security—to impose a range of economic sanctions. Prior to 2025, though, no president had ever imposed tariffs under IEEPA. Now that President Trump has, the Supreme Court’s decision in Learning Resources will determine whether IEEPA-based tariffs are lawful.

Trump has imposed (as opposed to merely threatened) four major sets of tariffs under IEEPA. In February, he targeted Canada, Mexico and China after declaring an emergency over fentanyl smuggling from those countries. On April 2, which President Trump dubbed “Liberation Day,” he imposed a 10% duty on imports from all countries, along with additional “reciprocal” tariffs on specific countries, to address trade imbalances. In July, Trump imposed an additional 40% tariff on Brazilian imports (on top of the 10% imposed as part of the Liberation Day tariffs) on the grounds that Brazil’s prosecution of its former president, Jair Bolsonaro, posed a threat to U.S. security. And finally, in August, Trump hit India with a 25% tariff on many imports in retaliation for India’s continued purchases of Russian oil while Russia prosecutes its war in Ukraine.

Although Canada has been subject to sector-specific tariffs, such as those imposed under Section 232 on steel and aluminum, these IEEPA tariffs contain exemptions that have to date insulated Canada from their worst effects. The ‘Liberation Day’ tariffs do not apply to Canada while the original “fentanyl” tariffs are in place, and the fentanyl tariffs contain an exemption for Canadian-origin products under the Canada-US-Mexico Agreement (CUSMA), although Canadian businesses could still be responsible for IEEPA tariffs on products they send to the US that are not of Canadian origin. If realized, though, Trump’s most recent threat would reflect a significant expansion of US tariffs on Canadian goods.

As a result, the Supreme Court’s decision in Learning Resources just became much more important to Canada. Every law that explicitly authorizes the U.S. government to impose tariffs contains at least some checks or limits. The most common is a requirement of some kind of investigation and factual findings before the government can act. IEEPA, though, does not mention tariffs explicitly nor does it require any investigation or findings, other than an unreviewable emergency declaration, before the president acts. That’s the attraction for Trump. If the Supreme Court rules that IEEPA authorizes tariffs, he can threaten Canada with tariffs on Saturday and impose them on Monday without any process to slow him down.

This lack of process in IEEPA — and the lack of any explicit reference to tariffs in the statute — has been the basis for over a dozen challenges to the IEEPA tariffs. The most significant of these cases to date is V.O.S. Selections v. Trump, which the Supreme Court will hear alongside Learning Resources v. Trump next week (the Supreme Court case is known by the latter name for shorthand). V.O.S. Selections itself combines two cases brought by small businesses and 12 U.S. states.

If the Supreme Court rules that IEEPA authorizes tariffs, Trump can threaten Canada with tariffs on Saturday and impose them on Monday without any process to slow him down.

In May, a three-judge panel of the U.S. Court of International Trade unanimously ruled the fentanyl and Liberation Day tariffs unlawful under IEEPA and issued an injunction to halt their collection. The Federal Circuit Court of Appeals upheld this ruling, citing, among other reasons, IEEPA’s lack of clear authorization for tariffs. Under the Supreme Court’s new “major questions doctrine,” Congress must have clearly authorized governmental action on issues of major political and economic significance. The tariffs are politically significant, of course; their economic magnitude dwarfs other policies that the Supreme Court has found significant; and since IEEPA does not say anything about tariffs, it does not clearly authorize them. A different trial court in Learning Resources reached a similar conclusion, and the Supreme Court granted review and consolidated the cases before the court of appeals ruled in that case.

Overall, then, three federal courts and a total of 15 federal judges across the various proceedings have considered whether IEEPA authorizes the fentanyl and Liberation Day tariffs. All three courts have concluded it does not, with only four judges on the Federal Circuit Court of Appeals dissenting from that conclusion.

Even if the Supreme Court agrees with the lower courts—and I filed a brief with the Court on behalf of U.S. trade law professors arguing that it should—tariffs are not likely to go away. The court of appeals in V.O.S. Selections sent the case back to the trial court to reconsider whether the trial court properly ordered the government to stop collecting the tariffs for all imports, or whether instead the order should only apply to the plaintiffs.

This might seem unimportant; if the tariffs are unlawful, then any plaintiff would be entitled to an order preventing their collection, which would normally result in the government stopping the collection of the tariffs on its own. But the Trump administration has tended to enforce court orders within the precise legal limits of the order. It is therefore not impossible that the administration will force plaintiffs to litigate the scope of the remedy the courts grant, rather than only the legality of the tariffs.

Similarly, parties that have paid unlawful tariffs—what are known as “importers of record”—should be in principle entitled to refunds. An administrative process exists to correct the amount of money owed, but the Trump administration could make that process sufficiently difficult that parties may need to file suit. Even if the Trump administration simply agrees to process refunds, only the importer of record is entitled to a refund. Whether subsequent purchasers, such as consumers or companies, are entitled to refunds depends on the terms of their agreements with the importer of record.

Finally, the Trump administration may simply reimpose similar tariffs under different legal authorities. In addition to Section 232, two other laws—Section 338 of the Tariff Act of 1930 and Section 122 of the Trade Act of 1974—could be used to reinstitute some or all of the IEEPA tariffs. Those laws have never been used before and contain different limits that have not been tested. But given the administration’s predilection for tariffs, it seems likely that it will look for other ways to keep tariffs in place.

For the same reason, the “trade deals” that the Trump administration has negotiated seem likely to remain in place, even if their terms may not be observed as scrupulously as before.

The legality of the deals themselves is not at issue in any of the cases filed to date, so the decision will not directly invalidate them. The only effect Learning Resources will have on the trade deals is potentially to limit the U.S. government’s ability to impose the higher tariffs that have spurred countries to negotiate with the United States.

Because the U.S. government has other means of imposing tariffs, it seems unlikely that other countries will walk away entirely from any agreements they reach with the Trump administration. But if the result of Learning Resources is a reduced ability to impose across-the-board tariffs at the drop of a hat, countries may slow down their efforts to reach new agreements or to implement the terms of any existing agreements with the United States. Parties relying on new market access granted to U.S. exports by those deals would thus do well to pay close attention to the diplomatic landscape following the Supreme Court’s decision.

Timothy Meyer is the Richard Allen/Cravath Distinguished Professor in International Business Law at Duke University School of Law.