The Supreme Court drew a schedule of tariff powers — then the administration used the box it had left blank

Executive summary

• On 22 August 2026, additional US tariffs of 50% on selected Canadian goods took effect, imposed under Section 338 of the Tariff Act of 1930 (Section 338 of the Tariff Act of 1930) — a provision that specialist law firms say “does not appear” ever to have been used to impose tariffs.
• The section runs to nine paragraphs and 6,608 characters. We read and scanned it in full: zero instances of the terms “expires”, “revoked”, “ceases”, “renewed”, “reviewed” or “report to Congress”.
• The real difference is not duration alone: Section 232 also has no expiry requirement. What distinguishes this delegation is the combination of an open-ended duration with no mandatory procedure — no investigation, notice, hearing, administrative body or report.
• The Supreme Court documented this itself. In its 20 February 2026 ruling, in a sentence on constraining the “amount and duration” of tariffs, it gave Section 2132(a) a cap and a 150-day time limit; Section 2253(e) a cap and a phase-down requirement; and Section 1338(d) a cap and nothing else. It then listed laws with “strict procedural requirements” — and Section 338 is absent from that list.
• A justice named it five months earlier. Justice Kavanaugh wrote in his dissent that other laws “may justify most — if not all — of the tariffs at issue”, listing Section 338 among them, and concluded that the president had “checked the wrong legislative box”.
• The instrument functioned as negotiating leverage, by its own terms. Its effective date was 19 August; on 18 August, the tariffs were suspended for three days because Canada — according to the presidential proclamation — “demonstrated a commitment to eliminating discrimination”. They took effect on 22 August when this did not occur.
• What the current tariffs do not cover: the two proclamations expressly exclude goods already subject to Section 232, and goods “covered by the World Trade Organization Agreement on Trade in Civil Aircraft”. Accordingly, tariffs now in force do not cover Bombardier aircraft; any measure against them requires a new presidential proclamation. Drones are expressly excluded from the exclusion.
• The market did not price permanence; it priced redistribution. The ETF tracking Canadian equities (EWC) moved −0.78% while the spread between the two ends of the list widened to 35.13 percentage points; the most exposed name, Magna, absorbed its entire loss — −7.19% — in the first session in which the tariffs applied.
• The Canadian dollar said nothing. It rose 2.40% against the US dollar, but the dollar fell against the other six currencies by an average of 2.56%; thus the Canadian currency's net response was approximately zero and ranked fourth of seven.
• The Canadian response is open-ended as well. The Canadian Department of Finance statement on measures covering 27.6 billion Canadian dollars, effective from 8 September, contains no expiry date or repeal conditions.
• No lawsuit had been filed as of 8 September 2026. The section has never been judicially interpreted, and the argument that it was implicitly repealed by subsequent legislation is a serious one with named proponents — not a fringe view.