In 1956, the Socialist faction in the Common Assembly of the European Coal and Steel Community put forth a wide‑ranging and unprecedented critique of the High Authority, the Community’s executive body. The faction’s move elicited harsh rebukes from the assembly’s Christian‑Democratic and Liberal factions and was the first instance of overt and coordinated transnational partisanship. This article argues that this bitter exchange would have been unthinkable under the High Authority’s previous president, Jean Monnet, who was widely admired by all factions. The Socialist critique encompassed a range of Community policies. Yet the personality of the new High Authority President, René Mayer, proved an important factor in this first exercise in transnational partisanship in the early history of European integration.