Complete Amazon FBA labeling guide for 2026. Learn FNSKU vs UPC, label sizes, placement, suffocation warnings, and how to avoid the most common labeling rejections at Amazon FCs.
The most common labeling confusion for new FBA sellers is FNSKU vs UPC. Here's the essential breakdown:
UPC (Universal Product Code): A universal barcode that identifies a product regardless of seller. If two sellers both have the same product, they share the same UPC. This leads to co-mingling — where Amazon might ship another seller's units as yours.
FNSKU (Fulfillment Network Stock Keeping Unit): A barcode unique to your seller account and that specific ASIN. When you apply an FNSKU, Amazon knows exactly whose inventory it is. This prevents co-mingling and ensures accountability in the event of returns or customer complaints.
For most sellers: always use FNSKU labels. The only exception is if you explicitly opt into Amazon's Commingled Inventory program — which carries risk.
Amazon's label requirements are specific:
• Minimum size: 1 inch × 2 inches (1" × 2")
• Maximum size: No strict maximum, but must fit within the largest flat surface of the product
• Barcode type: Code 128, Code 39, or ITF-14 are acceptable. QR codes are also accepted.
• Readability: The barcode must scan cleanly. Blurry, wrinkled, or faded barcodes will cause rejection.
• Color: Black bars on white background recommended. Avoid colored backgrounds that reduce contrast.
• Font: Human-readable text below the barcode is required (FNSKU, product name, condition)
For thermal printers, we recommend Zebra ZPL labels at 203-300 DPI. Inkjet labels may smear; always test before printing a full batch.
Where you place the FNSKU label matters:
• Must cover the original manufacturer barcode — or the original barcode must be made completely unscannable
• Do not place on transparent surfaces — labels placed on clear poly bags can shift or become unreadable
• One scannable barcode per unit — if multiple barcodes are visible, the FC scanner may read the wrong one
• Do not place on the bottom of the product — bottom placement makes scanning difficult during FC induction
• Label must remain scannable after packaging — if the product is poly-bagged, the label must be on the outside of the bag
The safest placement: flat, opaque surface, on the outside of the primary packaging, facing outward.
If your product is packaged in a poly bag with an opening of 5 inches or larger, Amazon (and US law) requires a suffocation warning printed on the bag. The warning must:
• Be printed in a font size proportional to the bag size (minimum 10pt for bags under 15 sq in)
• Be visible and legible
• Not be covered by labels or tape
• Read approximately: "WARNING: To avoid danger of suffocation, keep this plastic bag away from babies and children. Do not use this bag in cribs, beds, carriages or playpens. This bag is not a toy."
Pre-printed bags with suffocation warnings are available from suppliers and are the easiest solution for sellers who poly-bag in-house.
Amazon FC staff and automated scanning systems will reject shipments with these labeling errors:
1. Multiple visible barcodes — scanner reads the wrong code
2. FNSKU placed inside the poly bag — must be on the outside
3. Label on a curved surface — barcode doesn't scan flat
4. Wrinkled or bubbled label — barcode lines are distorted
5. Label printed at incorrect size — too small to scan reliably
6. Missing suffocation warning on qualifying bags — automatic rejection
7. Using the wrong FNSKU — applying a label for one ASIN to a different product
8. Expired labels — labels printed for a previous shipment plan applied to a new one
At QuickShipment, every unit is scanned after labeling to verify readability. This is the step most self-prep operations skip — and it's why we maintain a 99.8% acceptance rate.
There are two distinct labels in FBA prep:
Product (unit) label: The FNSKU label applied to each individual unit. This identifies the product to Amazon's system.
Box (carton) label: Generated in Seller Central after creating a shipment plan. Each box gets a unique Amazon FBA label (with a barcode). This label tells Amazon which shipment the box belongs to and which products are inside.
Important: box labels cannot be reused between shipments. Each shipment plan generates unique box IDs — printing old labels for a new shipment will cause confusion and potential rejection at the FC.
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