We have a customer who is requesting that we hold funds from an ACH deposit because they feel that it is not a valid deposit. Is there any problem with holding funds at the customer's request?

I would ask for clarification on the "don't think it is valid" and return, I would not hold. if it isn't valid now, it won't be tomorrow, or the next day, or however long they want a hold put on it.

Uh, the customer is in control here. If he does not spend the money, there will be no need for the hold, right?

You need to know exactly what's going on...

Agreed. Although I don't have any facts, my speculation based on the customer's concern is that they are likely being used as a money mule. (e.g. they were contacted to be a "payment processor" for their "employer" and have received stolen money via ACH that they are directed to wire to their "employer." I agree with Ken. We should be asking the customer questions instead of trying to figure out how to comply with this request.

Thanks for the comments. I had the same thought that we need to know just why they want the funds held and that they don't need us to hold the funds as they have control over them.