Based on French firm-level data, we evaluate the contribution of the micro-level profit-shifting –through tax haven foreign direct investments– to the aggregate productivity slowdown measured in France. We show that firm measured productivity in France declines over the years following the establishment in a tax haven, with an average estimated drop by 3.5% in apparent labor productivity. To isolate the contribution of multinational enterprises' (MNEs) tax optimization to the decline in productivity, we then exploit the 2006 Cadbury-Schweppes decision of the European Court of Justice limiting the extent to which member States can counter European MNEs' tax planning strategies. We find that multinational groups benefiting from that loosening of the legal constraints do exhibit a lower labor productivity following that ruling. Finally, given these firms' weight, our results imply an annual loss of 5.7% in terms of the aggregate annual labor productivity growth.