Flexible electricity networks continuously coordinate and optimize operations through ICT systems. An overlay data grid conveys information about the state of the electricity grid, including the real-time status of demand and production. Data is thus the basis for decisions that affect electricity costs and availability of assets. It is crucial that these decisions are formed and monitored according to a well-defined governance model. No such data governance model exists today. In this paper, we focus on data governance in virtual power plants. We define the problem, insisting on the issues linked to the inherent asymmetry of this system. We propose unionization as a framing device to reason about these issues. The central contribution of this paper is a set of principles for a unionized data governance model for virtual power plants.