Between Wednesday 11 March and Friday 13 March 2026, the Office of the US Trade Representative launched two separate Section 301 investigations that together represent the broadest trade-enforcement opening since the original China probe in August 2017. The first targets structural excess capacity in manufacturing across 16 countries including China. The second targets forced labour practices across 58 countries. Public comments close on 15 April, and a combined hearing has been scheduled for 28 April at USTR’s Winder Building office in Washington. If you import bulk chemical intermediates into the US, particularly MDI, TDI, polyols, caprolactam, melamine, PTA or soda ash, you need to file a comment, and you need to start modelling the tariff outcomes this week.
MOFCOM has already retaliated. On 27 March the Chinese Ministry of Commerce announced a reciprocal investigation into what it called “US discriminatory industrial subsidies” and placed three additional US chemical producers on the unreliable entity list. The rhetorical tempo is the closest we have seen to the April 2018 exchange that preceded the first Section 301 tariff wave, and the substantive overlap with chemicals is larger this time.
What the two investigations actually cover
The structural excess capacity investigation was initiated on 11 March under Section 302(b)(1)(A) of the Trade Act of 1974. USTR identified 16 countries whose state-linked industrial policy is alleged to produce capacity in excess of domestic demand, with the resulting oversupply dumped onto world markets at prices below long-run cost. The 16 countries named in the federal register notice include China, Vietnam, Thailand, Indonesia, Malaysia, the Philippines, Cambodia, Bangladesh, Pakistan, India, Brazil, Mexico, Turkey, Saudi Arabia, the United Arab Emirates and Russia. The sectors flagged for evidence collection include steel, aluminium, shipbuilding, solar, EV batteries, legacy semiconductors and, critically for our readers, “basic and specialty chemicals including polyurethane precursors, aromatic intermediates and commodity polymers.”
The forced labour investigation was initiated on 12 March under Section 307 authorities and Section 301 authorities in combination. It covers 58 countries and is explicitly designed to layer on top of the Uyghur Forced Labor Prevention Act enforcement framework rather than replace it. The federal register notice names Xinjiang-adjacent supply chains as a priority target and calls out solar polysilicon, cotton, tomato products, aluminium, electronics components and, again for our readers, “chemical intermediates manufactured in facilities with documented links to government-directed labour transfer programmes.”
The combined scope, 16 plus 58 countries, covers essentially every low-cost manufacturing base on the planet. That breadth is the point. USTR is no longer trying to draw a surgical line around Chinese state-linked overcapacity. It is building an evidentiary base that supports a tariff framework applicable at any origin where the structural conditions are found.
The timeline every importer should have pinned
| Date | Milestone | What it means for you |
|---|---|---|
| 11 Mar 2026 | Excess capacity investigation initiated | Federal register notice published; 30-day comment window opens |
| 12 Mar 2026 | Forced labour investigation initiated | Parallel federal register notice; same comment window |
| 27 Mar 2026 | MOFCOM retaliatory investigation announced | Three US chemical producers added to unreliable entity list |
| 15 Apr 2026 | Public comments deadline | Written comments due to USTR by 5pm ET |
| 20 Apr 2026 | Pre-hearing briefs due | Formal written positions from hearing witnesses |
| 28 Apr 2026 | Combined hearing, Winder Building | Oral testimony; USTR staff Q and A |
| 12 May 2026 | Post-hearing rebuttal comments due | Written responses to hearing-raised issues |
| Jul to Sep 2026 | USTR preliminary determination expected | Likely tariff schedule proposal if violation found |
| Oct to Dec 2026 | Final determination and tariff action | Actionable tariffs possible before year-end |
The compressed schedule matters. The original Section 301 China investigation in 2017 to 2018 ran roughly 9 months from initiation to first tariff list. If USTR hits the same cadence this time, importers should be modelling tariff implementation at some point in the final quarter of 2026.
Why MDI is sitting in the crosshairs
Methylene diphenyl diisocyanate, HS 2929.10.80, CAS 101-68-8, is the textbook example of what the excess capacity investigation is looking at. China added roughly 2.4 million tonnes of MDI capacity between 2019 and 2025, largely through Wanhua Chemical’s expansions at Yantai, Ningbo and the recently commissioned Fuzhou second line. Global MDI demand grew at roughly 4.5% per year over the same window. Chinese nameplate capacity by end-2025 stood at approximately 5.1 million tonnes. Domestic Chinese consumption absorbs roughly 3.2 million tonnes. The gap is a structural 1.9 million tonnes per year of export-destined MDI.
US MDI demand sits near 1.35 million tonnes. Domestic producers Dow, BASF, Covestro and Huntsman have combined nameplate of roughly 1.48 million tonnes with typical operating rates at 82 to 88%. Chinese imports into the US ran at 215,000 tonnes in 2025, largely from Wanhua directly and through its Louisiana JV. If USTR finds structural excess capacity in Chinese MDI, a tariff response in the 15 to 30% range is plausible.
The landed-cost consequence for a US formulator would be sharp. March 2026 Chinese MDI FOB Ningbo-Zhoushan ran at $1,680 per tonne. Ocean freight to Houston, $120 per tonne. Current Section 301 duty stack at 25%, plus MFN at 6.5%. Landed Houston, roughly $2,280 per tonne. If a new 25% ad valorem tariff lands on top of the existing Section 301 layer, the landed cost steps to $2,700 per tonne. That is a $420 per tonne shift, or roughly 18%, and it will move overnight when the tariff publishes in the federal register.
The forced labour overlay changes the risk model
Here is what most importers are getting wrong about the forced labour investigation. They read it as a China-only issue layered on top of UFLPA, and they assume their existing UFLPA due diligence covers them. It does not, for two reasons.
First, the 58-country scope means an importer sourcing from Uzbekistan, Turkmenistan, Malaysia, Vietnam, Cambodia, Bangladesh or Pakistan is now inside the same due diligence expectation that previously applied only to Xinjiang-linked goods. Second, USTR is working from a broader definition of forced labour than UFLPA alone, one that incorporates International Labour Organization indicators including deceptive recruitment, wage withholding, passport retention, restricted movement and excessive overtime. Your social audit needs to screen against all 11 ILO indicators, not just the government-directed labour transfer markers that dominate UFLPA enforcement.
For chemicals, three product families are drawing particular scrutiny. Polysilicon and its downstream silane and chlorosilane derivatives, given the existing Xinjiang solar linkage. Aluminium smelting and the associated bauxite, alumina and primary aluminium trade, where labour transfer evidence has been building since 2023. And specialty surfactants produced in Turkmenistan and Uzbekistan, where the cotton-adjacent supply chain has been flagged repeatedly by the ILO.
How to write a comment USTR will actually read
You have five weeks until the 15 April deadline, and a well-constructed comment is the single highest-impact document a mid-sized importer can produce this quarter. USTR’s Section 301 staff read comments. I have sat in on the post-comment debriefs twice in the last eight years, and I can tell you what moves the needle.
State your operational footprint up front. US headcount, US facility locations, annual US revenue, and the specific HS codes and CAS numbers you import in volume. A comment that opens with “we import approximately 8,400 tonnes per year of HS 2929.10 MDI into our Charlotte, North Carolina formulation facility, supporting 312 direct US jobs” gets read differently than a generic industry association boilerplate.
Quantify the tariff impact on end-user prices. If a 25% ad valorem tariff on Chinese MDI would push your spray foam insulation selling price up by 14% and your nearest domestic source cannot meet your 18,000 tonne annual volume requirement, say so with numbers.
Identify alternative sources honestly. If Korean MDI from Kumho Mitsui or Japanese MDI from Tosoh is a workable alternative and you can document the qualification timeline and cost, put it in. USTR uses this input directly when drafting exclusion frameworks.
Address the forced labour overlay even if your primary concern is excess capacity. A comment that acknowledges both investigations and shows your supplier qualification programme already screens against ILO indicators demonstrates the kind of operational maturity that USTR staff reward when building exclusion lists.
Three actions before Friday 15 April
Map your China-origin exposure by HS chapter and CAS number. If the chemical lines you flagged overlap with MDI, TDI, polyols, caprolactam, melamine, PTA, soda ash, aromatic intermediates or commodity polymers, you are inside the excess capacity investigation’s likely ambit. Calculate annual spend and tonnage.
Model the tariff scenarios. Build three cases at 10%, 20% and 30% additional ad valorem on top of existing Section 301 and reciprocal layers. Calculate landed-cost impact per tonne and annualised P and L exposure. Include the inventory build opportunity between now and any late-2026 implementation date.
File your comment by 15 April. If you are small enough that filing alone feels daunting, join a trade association comment and add a corporate annex with your specific numbers. The American Chemistry Council and the Society of Chemical Manufacturers and Affiliates are both organising co-ordinated filings this cycle.
The USTR twin-investigation opening is the most consequential trade-enforcement event of 2026, and it is happening on a four-month clock. Importers who engage the process between now and 28 April will shape the tariff schedule. The ones who wait for the final determination will be repricing their book in October under somebody else’s terms.