Announcement reposted from Amazon Japan:
Enterprise Customers at Amazon Business input Purchase Order Number (PO#) at checkout for their accounting purpose. They expect PO# to be printed on Shipping Labels without opening the boxes. To meet such needs, we started to print PO# on the shipping labels purchased through Buy Shipping at Seller Central (or Marketplace Shipping Service).
Find out Sample Label.
What is Buy Shipping?
Buy Shipping is a label service, where you can buy shipping labels individually or in bulk, ship and confirm your orders, and track your shipments. It automatically suggests shipping services based on services that can meet the delivery promise to the customer, your carrier preference, and lowest available cost. For more information about Buy Shipping, go to Use Buy Shipping services.
How to buy Shipping Label?
On the Manage Orders page, you can buy shipping either from the list view or from the order details. From your seller account, go to Orders > Manage Orders, and then click the Buy shipping button for the order you want to ship. You can also access the Buy shipping button from the Order details page by clicking the order number. For more information about how to buy shipping label, go to Buy shipping through Seller Central.