You can elect to participate in Amazon’s “Inventory Placement Service,” where Amazon will assign units of a single product/ASIN to a single fulfillment center. You are only responsible for sending your shipment to that one assigned fulfillment center; after the shipment arrives, Amazon will split it up and send it to different fulfillment centers for you. 

The default FBA service is “Distributed Inventory Placement” where Amazon may assign units of a single product/ASIN to multiple Amazon fulfillment centers when you create a shipment plan.

Can I choose which fulfillment center a product is assigned to?

No. Amazon will determine which fulfillment center a shipment of a product is assigned to. 

Does this service guarantee that my shipment won't be split into multiple fulfillment centers?

No. If you have multiple products/ASINs in one shipment, the shipment may still be sent to multiple fulfillment centers. If you have different unit types of a single product (ex. standard size vs oversize), they may be directed to different fulfillment centers. 

See Amazon’s Help Center for program fees and more information.