Tariff probes trigger immediate market and supply‑chain panic

The Trump administration reopened its tariff campaign in March by launching new trade probes that could lead to fresh duties on China, Mexico, Canada and other major trading partners. (ustr.gov) (reuters.com) U.S. Trade Representative Jamieson Greer announced on March 11 that his office was starting Section 301 investigations into 16 economies over “structural excess capacity and production” in manufacturing sectors. China, Mexico, Canada, the European Union, Japan, South Korea, India and Taiwan were on the list. (ustr.gov) (reuters.com) A day later, on March 12, USTR opened a second set of Section 301 cases covering 60 economies over failures to block imports made with forced labor. That list also included China, Canada and Mexico, and USTR scheduled public hearings and requested written comments. (ustr.gov) (federalregister.gov) These were not immediate tariffs. Section 301 is the trade law the United States uses to investigate foreign practices first, then decide whether to impose duties or other penalties later. (ustr.gov) (kelleydrye.com) The push came after the Supreme Court ruled 6-3 on February 20, 2026, that Trump could not use the International Emergency Economic Powers Act to impose his sweeping “reciprocal” and fentanyl-related tariffs. Chief Justice John Roberts wrote for the majority. (reuters.com) (scotusblog.com) That ruling blew a hole in Trump’s second-term tariff architecture. Reuters reported the new probes were designed to rebuild tariff pressure through a different legal path that is slower, more procedural and more likely to survive in court. (reuters.com) (cnbc.com) The manufacturing-capacity probe reached countries that account for large shares of U.S. imports in steel, autos, electronics and industrial goods. USTR said the inquiry would examine whether foreign policies create overcapacity that undercuts American producers and workers. (ustr.gov 1) (ustr.gov 2) The forced-labor cases were even broader. USTR said the 60 targeted economies were the largest U.S. trading partners and argued that weak import bans can give foreign goods an “artificial cost advantage” over domestic rivals. (ustr.gov) (kelleydrye.com) China answered with its own trade investigations in late March, according to Bloomberg, mirroring the U.S. legal strategy before an expected Trump-Xi meeting. That signaled the dispute was moving from campaign threats into formal tit-for-tat cases. (bloomberg.com 1) (bloomberg.com 2) By late April, Bloomberg reported that about $300 billion in goods subject to Trump-era tariffs were already reaching the United States through Southeast Asia and Mexico, underscoring how companies redraw supply chains when tariff risk rises. The March probes did not cause that rerouting on their own, but they showed Washington was preparing another round of trade fights through a sturdier legal route. (bloomberg.com) (supplychaindive.com)