The aim of the paper is to analyze the relation between information and parties’ influence on public opinion. The focus is on an heuristic process: the European Union is a political system that people can perceive as distant, compared with the national one, because of its complex functioning and of the less direct influence that citizens have on it; therefore, it is likely that people lack the relevant information for autonomously constructing their own idea of the integration process and, because of this, they rely on their preferred party’s stance on EU. Following this reasoning, political information should play a big role in determining the level of “independence” of electors’ judgement: people with more information do not need to rely on party positions and for this reason are more autonomous in expressing their level of support for European Union. The need for heuristics, however, can be measured not only based on voters' level of political sophistication, but also according with the level of complexity of the issue they are asked about: if people have to express their opinion on a complex issue, they will need more information and, consequently, they will be more likely to use party heuristic. Given its complex functioning and its perceived distance from citizens’ life, the European Union represents an issue where national political parties can be really influential in shaping people’s political attitudes. The paper uses cross-sectional as well as experimental data to investigate the relation between information and effectiveness of parties' cues.