29 CFR 548.401: Agreement or understanding.

If the agreement or understanding establishing the basic rate is in writing, whether incorporated in a collective bargaining agreement or not, a copy of the agreement or understanding should be attached to the application. If it is not in writing, however, the application to the Administrator for approval of a basic rate should contain a written statement describing the substance of the agreement or understanding, including the proposed effective date and term of the agreement or understanding. The term of the agreement or understanding may be of definite duration, or may run indefinitely until modified or changed. If an agreement or understanding is modified, a new application for authorization should be made. 19