We study the problem of freight pricing using pricing break points with quantity discounts offered by liner shipping services to freight forwarders in maritime transportation. We propose a model that maximizes the liner shipping and the forwarders profits. The forwarders book slots on the vessels for every trip (usually weekly) in a quantity that is encouraged by a pricing scheme proposed by the liner services with a single breakpoint. The booking is done before the forwarders have an accurate idea about their transport demands, and therefore they model it using probabilistic representations. Since container transportation services cannot be stored and given the stochastic nature of demand, the studied problem can be considered as a newsvendor type problem. Moreover, we consider an accurate formulation of the cost function of the liner service in which the sailing speed is a decision variable. The model is an integrated decentralized two-stage optimization model where the forwarders constitute the first stage and the liner company the second, and in which the optimal decisions taken by one stage are taken into account in the optimization of the decisions of the other stage. A numerical application is provided to show the effectiveness of the model.