Chapter 99 of the Harmonized Tariff Schedule is where the United States puts its temporary trade-remedy duties: Section 232 tariffs on steel and aluminum, Section 301 tariffs on goods from China, and the reciprocal tariffs that have reshaped import costs since 2025. The lines are numbered 9903, and they work differently from the rest of the tariff schedule: they layer an additional duty on top of the normal rate, they expire or change on short notice, and they are the lines a customs broker checks first, because they are the ones that move the total. An importer who classifies a product correctly in its normal chapter but misses the 9903 line has classified it wrong in the only way that costs money.
How a 9903 line works
A 9903 line is a temporary duty, added to the normal tariff rate for a specific product from a specific country, for a specific period. The line carries its own rate, its own product scope, and its own expiration, and it sits on top of the normal duty. A steel product classified in Chapter 72 might carry a normal rate of 0 percent and a Section 232 duty of 50 percent under a 9903.82 line, so the total duty is 50 percent, not zero. The 9903 line is the duty. The normal chapter is the classification.
The lines are organized by program. Section 232 steel and aluminum duties live in 9903.82, with the main line at 9903.82.02 and the program running from 9903.82.01 to 9903.82.26. The tiers are 50 percent for Annex I-A, 25 percent for Annex I-B, and 15 percent for Annex III, through December 31, 2027. The United Kingdom gets a 25 percent rate under 9903.82.04. Russian aluminum carries a 200 percent rate under 9903.85.67 and 9903.85.68. Each line has its own scope, and the scope is defined by the HTS heading, the product description, and the country of origin, so the same product from two countries can carry two different 9903 rates.
And the lines change. A proclamation can add a line, change a rate, or extend a program, effective on the date it specifies, not the date the importer learns about it. Proclamation 11021, issued April 2, 2026 and effective April 6, 2026, changed the Section 232 duty from a rate on the metal content to a rate on the full customs value, which doubles a duty overnight for an importer who was not watching.
Reading a 9903 line without missing the scope
The scope is the hard part. A 9903 line does not apply to every product in a heading, only to the products described in the line's text, which may be narrower, and to the countries listed. The steel and aluminum program has a 15 percent-or-less metal content de minimis: a product with 15 percent or less steel or aluminum content by value is outside the duty. An importer who does not know that rule pays duty on an exempt product, and one who applies it wrong underpays and faces a penalty.
The country of origin matters more in Chapter 99 than anywhere else in the schedule, because the 9903 rate is country-specific. The same steel product from the United Kingdom carries 25 percent, from most other countries 50 percent, and from Russia 200 percent for aluminum. The origin is determined by the substantial transformation test, a new name, character, and use, or by the tariff-shift rules for Canada, Mexico, and textiles, and a wrong origin claim costs the duty plus a 10 percent non-remittable marking duty and penalties under 19 USC 1592, plus 40 percent on transshipped goods. The 9903 line and the origin determination are two halves of the same calculation, and both have to be right.
And the 9903 lines interact with each other. A product can be subject to both a Section 232 duty and a Section 301 duty, and the duties stack. A product can be subject to a reciprocal tariff and a Section 232 duty, and the total is the sum. The importer who adds only the largest duty and forgets the others will underpay, and the underpayment will surface at liquidation, when CBP assesses the full amount plus interest. The right way to read a 9903 line is to read all of them, for the product, the country, and the program, and to add them up.
Keeping up when the lines move
The practical discipline is a weekly check. The Harmonized Tariff Schedule is updated by proclamation, by Federal Register notice, and by CBP guidance, and the changes are published in the Federal Register and on the USTR and CBP websites. An importer who checks the 9903 lines for their top ten products every week will catch a rate change before it hits a shipment. An importer who checks once a quarter will learn about it from the duty bill.
Work with the broker, not around them. The broker reads the 9903 lines for a living, and the importer's job is to give the broker the information the lines require: the product's composition, the metal content by value, the country of origin with the basis for the claim, and the classification. A broker who has to guess the metal content will guess wrong, and the importer will pay for it. And keep the records: the classification, the 9903 lines applied, the rate, and the basis for the origin claim, because when CBP audits the entry, the records are the defense.
Frequently asked questions
What is a 9903 line?
A temporary duty line in Chapter 99 of the Harmonized Tariff Schedule, where the United States puts trade-remedy duties like Section 232 steel and aluminum tariffs and Section 301 tariffs on goods from China. The line layers an additional duty on top of the normal tariff rate.
What are the current Section 232 rates?
Under Proclamation 11021, effective April 6, 2026, the duty is on the full customs value: 50 percent for Annex I-A, 25 percent for Annex I-B, and 15 percent for Annex III, through December 31, 2027. The United Kingdom gets 25 percent, and Russian aluminum carries 200 percent.
Can a product be subject to more than one 9903 duty?
Yes. A product can be subject to both a Section 232 duty and a Section 301 duty, and the duties stack. The importer has to read all the applicable 9903 lines for the product, the country, and the program, and add them up.
How often do 9903 lines change?
On short notice, by proclamation or Federal Register notice. A proclamation can add a line, change a rate, or extend a program, effective on the date specified. Importers should check the 9903 lines for their top products every week.