Parliamentary european affairs committees (eacs) are the most important specialised body for scrutinising european union (eu) matters. Despite a central position in domestic policy-making, their role is often limited. In spain, the pre-eminence of the executive over the legislature is commonly assumed. This article applies moravcsik's four causal mechanisms for executive influence (initiative, institutions, information and ideas) to the analysis of reporting and debate on trans-european networks (tens) policy. Placing a microscope over the process of eu policy formulation, throughout which member states articulate their preferences, it seeks to understand why the executive might exert strong influence and the legislature remain weak.