The axiom of Balanced collective contributions is introduced as a collective variant of the axiom of Balanced contributions proposed by Myerson (1980). It requires that the identical average impact of the withdrawal of any agent from a game on the remaining population. It turns out that Balanced collective contributions and the classical axiom of Efficiency characterize the equal allocation of non-separable costs, an allocation rule which is extensively used in cost allocation problems and in accounting. For instance, the equal allocation of non-separable costs coincides with the Nucleolus on the class of data sharing games within the European REACH legislation. While our result does not hold on data sharing games, we provide comparable characterizations of the equal allocation of non-separable costs and the Shapley value.