This paper proposes a method which assists the firms for cooperating in make-to-order production. We especially focus on the operational decision levels of manufacturing companies : the forecast scheduling and the real-time scheduling. The method organizes a production process which is distributed over several companies, by lowering the production stocks with the aim of decreasing production costs. In the selected approach, the global organization is achieved progressively by a set of cooperations between pairs of actors of the supply chain. We study in particular the customer/supplier relationship for which the cooperation process concerns the attributes of the orders transmitted by the customer to the supplier. We assume that the relation is governed by a cooperation contract which defines a more contractual framework to the cooperation between the decision-makers. Our objective is to design support tools that assist them during this cooperation process.