We introduce a behavioral contract theory idea, “shading” (Hart and Moore (2008). “Contracts as Reference Points.” Quarterly Journal of Economics 123 (1): 1–48)) as a component of ex-post haggling (addressed by Coase (1937. “The Nature of the Firm.” Economica 4 (16): 386–405) and Williamson (1975. Markets and Hierarchies: Analysis and Antitrust Implications. New York: Free Press)) into the collusion model à la Tirole (1986. “Hierarchies and Bureaucracies: On the Role of Collusion in Organizations.” Journal of Law, Economics, and Organization 2 : 181–214, 1992. “Collusion and the Theory of Organizations.” In Advances in Economic Theory: The Sixth World Congress, edited by J. J. Laffont. Cambridge: Cambridge University Press), thereby constructing a new model of hierarchical organization. By integrating the two ideas, i.e. collusion and shading, we enrich the existing collusion model, thereby obtaining a new result for Collusion-proof versus Equilibrium Collusion. The basic idea is that the increase in shading pressure strengthens the incentive for collusion, thereby making it difficult to implement collusion-proof incentive schemes, which leads to the Equilibrium Collusion. In addition, we also provide a micro-foundation for ex-post haggling costs, where we view rent-seeking associated with collusive behavior and ex-post haggling generated from aggrievement and shading as the two sources of the costs. This model is used to examine the optimal organizational design problem as an optimal response to the trade-off between gross total surplus and ex-post haggling costs, and to take a step further the idea of efficient organization design (Milgrom (1988. “Employment Contracts, Influence Activities and Efficient Organization Design.” Journal of Political Economy 96 : 42–60)). We believe that our model could help provide a deep understanding of resource allocation and decision processes in hierarchical organizations.