The left-right line of conflict has been the dominant dimension of decision-making in the European Parliament since 1979. A pro-/anti-European Union integration dimension is of secondary importance. Limited evidence exists on the conditions under which these different dimensions matter. This study examines parliamentary decision-making about the so-called Two-Pack, which moved responsibilities about budgetary decision-making to the European Commission. The article uses in-depth interviews, textual analysis of committee debates and roll call voting analysis in order to determine which lines of conflict matter at which stage of decision-making. The evidence indicates that left-right division is dominant in the informal stage preceding committee debates, while both the pro-/anti-European Union and the left/right dimensions matter during the committee stage, whereas for plenary votes, the pro-/anti-European Union dimension is crucial.