Previous research has shown that if countries ”merge”, (i.e. move to centralized policy choices) the effect is to reduce lobbying. However empirical evidence suggests that this is not the case. This paper explains the empirical evidence in a two-jurisdiction political economy model of public good provision under policy centralization and policy decentralization, where the policy choice can be affected by the pressure of endogenously formed lobbies. We measure lobbying in three ways:(i) the number of lobbies formed under the two settings, (ii) their impact on policy decisions and (iii) the amount of resources transferred to the policy makers. We show that preference heterogeneity and lobby formation are positively related and that moving from decentralization to centralization can affect both the number and the type of lobbies. We develop some examples; among them: under centralization, compared to decentralization, the size of lobbies can be higher but the impact on policy can be smaller. Moreover we show how the majority groups try to offset lobbying by strategic voting for a candidate of a different group.