The International Emergency Economic Powers Act (IEEPA) gives the President certain powers “to deal with any unusual and extraordinary threat” to the country’s national security, foreign policy, or economy. Although the statute doesn’t explicitly grant authority to impose tariffs, President Trump announced a set of sweeping tariffs in April 2025, triggering a global stock market crash. Trump argued that IEEPA implicitly authorized his actions—a claim no prior president had ever made in the statute’s nearly fifty-year history.

Learning Resources, Inc., an educational toy manufacturer, successfully challenged Trump’s tariffs in the United States District Court for the District of Columbia. Although the Trump administration appealed to the Court of Appeals for the D.C. Circuit, Learning Resources asked the Supreme Court to hear the case before the appellate court could rule. Separately, a group of small businesses led by V.O.S. Selections and a coalition of twelve states successfully challenged the tariffs in the United States Court of International Trade. On appeal, the Federal Circuit upheld that decision, holding that IEEPA does not authorize the sweeping tariffs that Trump imposed. The Supreme Court consolidated the two cases and agreed to expedited review.

In October 2025, the Constitutional Accountability Center filed an amicus brief supporting the challengers to the tariffs. Our brief responds to a historical argument made in support of the tariffs. According to this argument, IEEPA incorporates a traditional presidential authority to impose tariffs during wartime that traces back to the nineteenth century and was first codified in the Trading with the Enemy Act of 1917 (TWEA). As our brief shows, this narrative is unsound.

When the TWEA was enacted, there was no consensus about the existence of an inherent presidential authority to impose tariffs during wartime. During the nineteenth century, every imposition of presidential duties or fees in wartime generated significant constitutional controversy. Rather than demonstrating any consensus, these historical episodes reveal fierce contestation over the President’s inherent wartime authority to impose tariffs. When the Supreme Court addressed challenges to these tariffs, the Court ultimately relied on Congress’s express approval of them—leaving the separation-of-powers dispute unresolved.

We further show that, regardless of the original TWEA’s meaning, Congress later severed the Act from its war powers foundation, and IEEPA further separated peacetime emergency powers from implied wartime powers in 1977. Even assuming that law-of-war principles recognized a wartime tariff authority in 1917, and that those principles were codified in the original TWEA, that doesn’t mean that the TWEA continued to confer this authority even after it was subsequently amended. On the contrary, amendments to the TWEA in 1933 dissolved any link with wartime powers and implied tariff authority.

Moreover, when passing IEEPA in 1977, Congress recognized that decades of amendments to the Act had created a dangerously broad grant of authority. Congress’s solution was to split the statute in two: the TWEA would apply only during declared wars, while the newly enacted IEEPA would cover peacetime national emergencies with more limited grants of power to the President. Far from expanding presidential authority, Congress deliberately constrained it. Because IEEPA applies to peacetime emergencies—not wars—any claimed wartime tariff authority has no place in the statute.

The decisions of the lower courts should be affirmed—President Trump doesn’t have authority under IEEPA to single-handedly set global tariffs.