Welcome to Preventive Controls in Human Foods!
One of the Preventive Controls measures is "Supply-Chain Preventive Controls" programs.
As a warehouse, you are definitionally part of the supply chain. IF the people using YOUR services determine through THEIR hazard analysis that YOUR facility and functions may pose a significant risk to THEIR product, they need EVIDENCE that you are adequately minimizing those risks.
How do they know you are receiving materials properly? Checking for sealed incoming shipments? Checking for damage, signs of pests, correct lots and items received, etc.?
How do they know you have a clean and sanitary facility? How do they know you adequately control for allergen hazards (and other separation concerns like kosher, halal, organic, etc.)
How do they know you pick and pull the right stuff? Make sure the right things go to the right customers in the right quantities?
Do you do any relabeling for your customers? That's a processing step, and often regarded as a critical control point. How do they know you put the right label on the right bag and didn't introduce a hazard like incorrectly declared allergens at this step?
Do you receive in any damaged or returned from customers items? How are you managing that? How do they know that your storage of damage prevents cross contact as well as prevents accidental shipment of on hold items?
(and so on).
Everyone is going to have to get WAY more comfortable in dancing WAY closer. The only way that you can satisfy the requirements of the customer asking how you do all that stuff up there is to provide them with examples of your programs and evidence that you are DOING all that stuff and doing it RIGHT.
You will be sending out a metric buttload more documentation. Also, non-conformances in the supply chain will REQUIRE a WRITTEN root cause analysis as well as a 30 day verification of effectiveness report.
GOOD TIMES AHEAD!!