Written by Marcus Rivera — Former Amazon warehouse ops, processed FBA shipments for 5 years. More about me →
Written by Marcus Rivera — Former Amazon warehouse ops, processed FBA shipments for 5 years. More about me →
I processed incoming FBA shipments at an Amazon fulfillment center for five years. I rejected hundreds of boxes and individual units because of barcode problems — wrong label type, unreadable print quality, barcode placed over a seam, FNSKU covering the UPC, wrong barcode for the ASIN. When your shipment gets rejected at an Amazon receiving dock, it doesn't just delay your inventory — you might incur inbound defect fees, and repeat offenders can have their shipping privileges suspended. Here's exactly what you need to get right.
Amazon's FBA system primarily uses FNSKU (Fulfillment Network Stock Keeping Unit), not the manufacturer UPC. The FNSKU is an Amazon-generated identifier that starts with "X" followed by 10 characters. It links the physical product in the warehouse to your specific seller account — so Amazon knows that this particular unit of a product belongs to you, not to another seller listing the same ASIN.
When you create an FBA shipment in Seller Central, Amazon generates FNSKU labels for each product. You print these labels and apply them to each unit. The FNSKU label must cover or replace the original manufacturer barcode — if both the UPC and the FNSKU are visible, the scanner might read the UPC instead, and the inventory routing breaks. I've personally handled shipments where the seller placed the FNSKU label next to the UPC instead of covering it. Every unit had to be manually relabeled by Amazon at the seller's expense.
Exception: if you're enrolled in Amazon's "commingled inventory" program, your products are mixed with other sellers' identical products. In that case, the manufacturer UPC is used and no FNSKU label is needed. But commingled inventory introduces its own risks — if another seller sends in counterfeit units, your inventory gets mixed with theirs. I recommend stickerless commingling for commodity products only.
Amazon's FBA labeling requirements per Seller Central (2026): labels must be printed on white, non-reflective thermal or laser labels, 1×2 inches minimum for small items, 2×3 inches for standard items. Print resolution must be at least 203 DPI. Barcodes must have at least 0.25 inches of white space on all sides (this is the quiet zone — they call it differently but it's the same thing).
From my experience on the receiving dock: the #2 rejection reason after wrong barcode placement was print quality. Inkjet-printed labels on glossy paper were the worst offenders. The scanner tunnel at Amazon reads barcodes at 600 feet per minute — if the barcode isn't crystal clear, it won't read at that speed. Use a thermal printer (Zebra, Rollo) or a quality laser printer on matte labels.
Every outer case and pallet also needs Amazon shipment labels. These are the larger barcodes (4×6 inches) with shipment IDs. These labels are generated during the shipment creation process in Seller Central, not through a general barcode generator. The barcodes on these labels are Code 128 format, which you can verify with GenBarcode's scanner before shipping. I've seen entire pallets rejected because the outer label had a single smudged digit — the scanner read the Shipment ID wrong, and the system couldn't reconcile the pallet with any active shipment.
Before you ship, test: scan every FNSKU on every unit, verify against your shipment plan, and check placement. Five minutes of testing prevents days of inbound defect resolution. Generate your product UPCs using GenBarcode's free generator for your GS1 prefix, then let Amazon's system convert those to FNSKUs during shipment creation.
Written by Marcus Rivera — Former Amazon warehouse ops manager. Rejected shipments at an FBA receiving dock for 5 years. These are the mistakes I saw that you can avoid. More about me →