An FNSKU is the barcode Amazon uses to tie a unit in its warehouse to one seller’s account. Amazon calls it simply the “Amazon barcode”, and it usually starts with X00. For years many brands skipped it and shipped products with only their UPC. Two changes in 2026 decided who can still do that.
- January 1, 2026: Amazon stopped prepping and labeling inventory for US FBA sellers. If your units arrive without the right labels, Amazon won’t fix them for you anymore.
- March 31, 2026: Amazon ended commingling. Customers now get units from your own inventory, and resellers must put an FNSKU on every unit.
This guide covers what an FNSKU is, whether you still need one, how to print and place it, and what happens when labels go wrong.
What an FNSKU Is, and How It Differs From Your Other Codes
| Code | Who issues it | What it identifies |
|---|---|---|
| UPC, EAN, JAN, ISBN | GS1 (brand owners buy GTINs there) | The product itself, everywhere it is sold. Amazon calls these manufacturer barcodes. |
| ASIN | Amazon | The product page on Amazon. Reviews and ratings live here. |
| FNSKU | Amazon | Your units of that product in Amazon’s fulfillment network |
| SKU | You | Your internal code for the offer |
The difference that matters: many sellers can share one ASIN and one UPC, but each seller’s FNSKU is their own. That is how Amazon knows whose inventory a unit is. Changing your SKU or FNSKU does not touch your reviews, because reviews belong to the ASIN.
Do You Still Need FNSKU Labels in 2026?
It depends on whether you own the brand. Since March 31, 2026 the rules look like this:
- Brand owners can go stickerless and use the manufacturer barcode, but only if all three of these are true: the product is new, it has a single scannable UPC, EAN or ISBN that matches one ASIN, and the product is registered to your brand in Brand Registry. Enrolling your brand does not register every product automatically.
- Resellers need an FNSKU on every unit, including authorized resellers and products that already carry a UPC.
- Products with a GTIN exemption must use an FNSKU.
The penalty for getting this wrong is real. Amazon treats reseller units that arrive without an FNSKU as defective. It relabels them, records it on your Inbound Performance Dashboard, and those units are not eligible for reimbursement. Stickerless stock that was already in a fulfillment center before March 31 keeps selling as it is.
Why Amazon made the change: commingling meant a customer could receive another seller’s unit of your product. Brands had complained about it for years, and Amazon estimated brands spent about $600 million in a single year re-stickering inventory to avoid it.
How to Switch a Product to Stickerless
- Confirm you are listed as the Brand Representative in Brand Registry.
- Check that the product is registered to your brand, not just sold under it.
- Make sure the product carries one scannable manufacturer barcode that maps to one ASIN. Multi-packs and bundles often fail this test.
- Change the barcode preference in Seller Central. Amazon says the change takes about 24 hours and applies only to new offers.
If any step is unclear on a large catalog, check the listings one by one before your next shipment rather than after. Our Brand Registry explainer covers the registration side.
How to Print FNSKU Labels in Seller Central
There are two places to print them:
- Send to Amazon: use Print SKU labels, or Print all SKU labels at the end of step 1. You can also reprint from View contents in the later steps.
- Manage Inventory: choose Print item labels on the product.
You can also print the FNSKU directly onto your packaging, as long as it follows the same size, white space and content rules as a label.
FNSKU Label Specs
| Requirement | Amazon’s rule |
|---|---|
| Size | Between 1 x 2 in and 2 x 3 in |
| Look | Black ink on white, non-reflective labels with removable adhesive |
| White space | 0.25 in on the sides and 0.125 in top and bottom, around the barcode and the label edge |
| What it shows | The FNSKU or ASIN, the product name and the condition |
| Printer | Thermal preferred, laser fine, no inkjet, at least 300 DPI |
| Durability | Must stay scannable for 24 months |
| Laser sheets | 21, 24, 27, 30, 40 or 44 labels per sheet; set printer scaling to None or 100% |
A practical tip: Amazon specifically says to set printer scaling to None or 100%. A PDF printed at “fit to page” can shrink the barcode enough that it fails to scan at the warehouse. Print one sheet, test a label with a barcode scanner app, then run the batch.
Where to Put the Label
- Cover every other visible barcode on the unit, so the scanner can only read the FNSKU. Don’t cover Transparency codes or serial-number barcodes.
- Keep labels off curves and corners, and at least 0.25 in from the packaging edge.
- The label must still scan after prep. If a unit goes in a poly bag, the label goes on the bag or has to scan through it.
- Case packs: every unit inside gets its own FNSKU, and barcodes on the outer case are removed or covered.
- Sets: items sold together need a “Sold as set” or “Do not separate” label so the warehouse doesn’t split them.
- Poly bags with an opening wider than 5 in need a suffocation warning.
What Happens When Labels Go Wrong
Amazon’s labeling errors fall into a few types: barcode missing, unit mislabeled, barcode can’t be scanned, and prep errors. Since Amazon no longer labels or preps US inventory, the fix is no longer a small per-unit fee. Units that arrive unprepped or unlabeled can’t be reimbursed if they end up damaged or untraceable. Amazon’s help pages also warn of unplanned prep service fees when shipments fail requirements.
Watch out for one common mix-up. Amazon’s “inbound defect fee” is not a labeling fee. It covers shipments that are misrouted, deleted or abandoned, and since January 15, 2026 it’s a single per-unit fee by size tier. Blogs that call it a labeling penalty have it wrong.
Labeling at Your Factory or at a 3PL
With Amazon out of the labeling business, someone in your supply chain has to own it. Three setups work:
- Your factory prints the FNSKU on the packaging. This is the cheapest per unit, but you need final FNSKUs before production, and a new FNSKU means new packaging.
- Your factory applies labels you send. It’s flexible, but check the first carton yourself.
- A 3PL or prep center labels on arrival. It adds cost and a handling step, but it’s the easiest option for resellers and mixed catalogs.
Whichever you choose, write down who applies labels, who checks them and what happens when a label fails. That becomes part of your inventory and logistics process, not a one-off task. If you also fulfill Walmart or Shopify orders from FBA stock, the same units flow through Multi-Channel Fulfillment, so labeling mistakes spread to every channel.
FNSKU Questions, Answered
Do I Need an FNSKU if My Product Already Has a UPC?
Only if you’re a reseller, or a brand owner whose product doesn’t meet the stickerless conditions. Brand Representatives with new, registered, single-barcode products can use the UPC instead.
Will Amazon Label My Products for Me?
Not in the US anymore. Amazon ended its prep and labeling service for shipments created on or after January 1, 2026.
Will a New FNSKU Reset My Reviews?
No. Reviews and ratings belong to the ASIN, not to your SKU or FNSKU.
Can I Print the FNSKU on My Box Instead of Using a Sticker?
Yes, as long as it follows the same size, white space and content rules as a label.
Labeling mistakes are one of the easiest ways to lose money quietly in FBA. If you want a second set of eyes on your inbound process before Q4, book a free Amazon audit and we’ll check your barcode setup along with your listings, ads and inventory.
Sources: Amazon Seller Central help, “FBA Barcode Choice and Labeling FAQ”, “Use Amazon barcodes for FBA”, “Use manufacturer barcodes”, “FBA Prep Service” and “Inbound defect fees” (checked September 27, 2026); Modern Retail, “Amazon to end commingling program” (September 17, 2025); Amazon, “FBA packaging, prep and labeling” (July 7, 2026). Amazon updates these rules often, so confirm details in your own Seller Central before a shipment.
