Supreme Court: President Cannot Use IEEPA to Impose Tariffs

The most consequential US economic ruling of 2026 came from the Supreme Court, not the Federal Reserve. On 20 February 2026, the Court ruled that the President cannot use the International Emergency Economic Powers Act (IEEPA) — the 1977 statute that gives the executive sweeping authority to regulate international transactions during national emergencies — to impose tariffs.

What the case was about

The Trump administration's 2025 tariff stack relied heavily on IEEPA as the legal anchor. The 10% "reciprocal" tariff, the 20% "fentanyl" tariff on China, and various country-specific tariffs were all grounded in declarations of national emergency and IEEPA authority. Multiple lawsuits — by importers, foreign governments, and industry associations — challenged that architecture, arguing that IEEPA was never intended to authorise the broad imposition of tariffs.

The Court agreed. In a textually grounded opinion, the majority ruled that IEEPA's enumerated powers — to regulate, prohibit and freeze transactions — do not extend to imposing customs duties. Tariffs, the Court held, require explicit congressional authorisation under the Constitution's foreign-commerce clause and the dedicated tariff statutes Congress has actually enacted.

What was struck down

The 2025 IEEPA tariffs are now unlawful. That includes the 10% reciprocal layer, the 20% fentanyl tariff and a number of country-specific tariffs that had been imposed during the year. The ruling did not affect tariffs imposed under other statutory authority — Section 232 national-security tariffs, Section 301 unfair-trade tariffs, Section 122 balance-of-payments tariffs, and the standard customs schedule — which remain in force.

The administration's response

Within days of the ruling, the Trump administration began substituting non-IEEPA tariffs. New investigations were launched in March 2026 under Section 301 against China, Vietnam, Taiwan, Mexico, Japan, the European Union and dozens of other economies. Section 232 reviews — which require the Commerce Department to find that imports threaten national security — were initiated for several product categories. Section 122 tariffs, which can be imposed for up to 150 days to address balance-of-payments emergencies, were used as bridge measures.

The substitution strategy works but is slower and more procedurally constrained than the IEEPA approach. Section 301 investigations typically take months. Section 232 cases require a formal Commerce Department report. Section 122 tariffs are time-limited.

What it changes

For trading partners, the ruling provides predictability. Tariffs imposed under Sections 232, 301 and 122 are anchored in statutes that have been used for decades, with established procedural rules and judicial review pathways. For the administration, it makes the trade war slower to wage but does not stop it.

For Congress, the ruling reinforces the importance of the legislative branch's tariff authority — and creates new pressure to update the foundational statutes if the executive's preferred speed of action is to be preserved.

The deeper question

Whether the Supreme Court's ruling produces durable constraint on executive tariff authority depends on what comes next. If Congress moves to delegate broader tariff power explicitly, the constraint dissolves. If subsequent administrations stretch Section 232 or Section 301 in ways the Court would similarly find unlawful, more litigation follows. For now, the ruling is the clearest reassertion of legislative tariff authority in a generation.