Résumé : In Belgium, 2007 has been marked by long coalition negotiations over an agreement on a new government. The main bone of contention had been related to the reform of the Belgian Federal State. Among the suggested reforms, the regionalisation of the collective bargaining system turned out frequently. It relies on the assumption that the productivity differences between regions are not fully taken into account in a federal wage setting system. Our findings challenge this hypothesis by putting forward the current existence of wage differentials between regions and joint committees. We also show that regional wage differentials at the joint committee level are correlated to regional productivity differences. Finally, we find that the correlation between regional wage differentials and productivity is higher in decentralised joint committees. Hence, we conclude that productivity variations are already integrated in the Belgian wage setting system.