To support rapidly evolving business models, communications network management systems are increasingly being federated to provide more flexible, end-to-end service management. In the future, such federation will need to be achieved dynamically, thus management systems will need to incorporate capabilities supporting negotiation of federations and management of their lifecycle. We discuss how federations can be governed via negotiated federation-level policies, that should be consistent with the relevant local policies of individual federation members. We describe a policy authoring process, outlining the steps to be taken when local or federation-level policies are created, modified or withdrawn. As this process depends on the presence of a rich system model for policy analysis we describe an extension to DEN-ng that models governance of federated domains. Finally, we outline a case study relating to inter-organisation XMPP federations to illustrate the policy authoring process.