We give necessary conditions for a neutral social choice function to be partially implementable by means of a strong equilibrium (i.e., implementable by cooperative agents): the veto power of the various coalitions should be maximally distributed. If moreover the social choice function is veto-anonymous, then the veto power of a coalition must be (roughly) proportional to its size: x per cent of the agents have the power to veto x per cent of the candidates. The procedure of "voting by successive veto" is an example of a neutral and (nearly) veto-anonymous social choice function which is implementable.