Recent research on interest groups and their access to Parliament have improve our understanding about this interaction. Analyzing mainly interest groups testimonies in parliamentary committees, previous research has showed that institutional factors are important to understand the dynamics of interest groups interaction with MPs. We know less though about, when and which parliamentary groups and interest groups interact in the amendment process.  The goal of this paper is to contribute to this research analyzing why interest groups devote resources to the amendment process. We will study if they contact only those parliamentary groups closer to their own preferences, or do they act strategically and contact all parliamentary groups. In addition, we want to investigate to what extent different typologies of interest groups behave differently. For instance, are advoacy groups more ideollogically centered than other type of interest groups when they look to influence the final redaction of a parliamentary law. We depart from in-deep interviews with MPs and interest groups to do the analysis.