This paper studies the political economy of growth in an economic union such as the EU. In the spirit of Acemoglu, Aghion and Zilibotti [Acemoglu, D., Aghion, P. and Zilibotti, F., 2006a, Distance to frontier, selection and economic growth, Journal of the European Economic Association, 4:1, 37–74; Acemoglu, D., Aghion, P., and Zilibotti, F., 2006b, Growth, development and appropriate versus inappropriate institutions, mimeo MIT.], as the economy approaches the world technology frontier, structural reforms that increase competition in intermediate goods sectors are necessary to boost innovation and productivity growth. Reforms, however, raise the opposition of incumbents and, therefore, are politically difficult to implement. When there are important cross-border policy spillover effects, national governments are more easily captured by vested interests, as they fail to internalize the benefits of reforms on the rest of the union. In this situation, productivity growth may be sluggish and the economy can fail to converge to the frontier. On the other hand, when policy is chosen by a union government (or a collective body that takes into account union welfare), the internalization of spillovers raises the perceived benefit of reforms and, consequently, lowers the ability of lobbies to obtain high levels of protection.