Why do legislators amendment executive bills? Evidence from a multilevel parliamentary system

Amendments are a crucial part of the legislative process. Individual legislators and parliamentary groups use them to influence policy outcomes, address technical issues, and signal to voters. Large-N empirical analysis of legislative amendments however are scarce, and in turn, we still know very little about the conditions under which legislators engage in amending legislation. We assembled a large dataset of all amendments introduced to all executive bills in Spain between 1996 and 2019, a total of 93.722 amendments to 808 bills. We then test whether variations on amending legislation respond to an ideological logic, legislative agreements, supranational constraints, issue preferences, political conflict, and asymmetries regarding resources and expertise. Interestingly, we find that in this multilevel parliamentary system neither the ideological distance among parties nor the regional content of legislation are predictive of a party introducing amendments. Instead, amendments are a reflection of bargaining dynamics: formal long-term agreements with the governing party translate into fewer amendments, while ad-hoc agreements to pass particular pieces of legislation translate into more. Moreover, legislative groups often use amendments to emphasize their positions on divisie issues. More amendments are introduced on complex and divisive bills, even if related to the EU, a generally consensual topic in Spain given that no hard euro skeptical positions exist in the party system. Yet, results show that not only political conflict and partisan politics matter. The resources at hand are also predictive of introducing amendments, including the size of the groups but also their portfolio of previous unsuccessful bills. Amendments are also more likely to be introduced if committee hearings are organized along the legislative process, signaling that amendments respond also to an informational logic. Overall, the study provides illuminating insides on the lawmaking process and puts forward a theoretical and empirical framework to better understand legislative dynamics in multilevel parliamentary systems.