Iowa Admin. Code r. 875-217.52
A tip is a sum presented by a customer as a gift or gratuity in recognition of some service performed for the customer. The payment is to be distinguished from payment of a charge, if any, made for the service. Whether a tip is to be given, and its amount, are matters determined solely by the customer, and generally the customer has the right to determine who shall be the recipient of the gratuity. In the absence of an agreement to the contrary between the recipient and a third party, a tip becomes the property of the person in recognition of whose service it is presented by the customer. Only tips actually received by an employee as money belonging to that employee, which the employee may freely use absent of any control by the employer, may be counted in determining whether the employee is a "tipped employee" and in applying the provisions which govern wage credits for tips.
Iowa Admin. Code r. 875-217.52
29 CFR 531.52.