Abstract : Air traffic generates workload for the air traffic controllers in charge of the airspace. For a large airspace, a single air traffic controller is not able to manage all this workload and the airspace is divided into sectors, each of them being assigned to a controller. When the traffic demand is decreasing during the night, the sectors are gathered together into groups to reduce the number of controllers in operation. Nowadays, this regrouping is performed empirically by airspace experts. In this paper, we show how the branch-and-price method can be used to compute a balanced grouping of air traffic control sectors to optimally reduce the number of controller teams during daily low flow periods.