This paper is dedicated to an axiomatic study of the Myerson value for cooperative

games in which the set of feasible coalitions is a union-stable system. This type of partial

cooperation structure generalizes well-known communication graph games and contains the

widely studied union-closed and voting structures. In this framework, we provide a simple

and intuitive characterization of the Myerson value using five appealing and independent

axioms. We show that the Myerson value is the only allocation rule on the set of union-stable

structures that satisfies component-efficiency, additivity, modularity, the extra-null player

property, and equal treatment of veto players. We also show that this characterization is

valid for the restricted class of union-closed structures.

Key words: TU-game, Union-stable structure, Harsanyi dividends, Harsanyi power

solution, Myerson value.