Law-making is a core function of parliaments in democratic systems. Yet we still know little about the extent to which parliaments influence legislation and the reasons why MPs prioritize some bills rather than others. We analyze the degree of bill amendments operated by parliament, by comparing bills before and after parliamentary deliberations with a text reuse approach. We postulate that MPs attempt to overcome the problem of limited processing by prioritizing certain bills over others, and rely on considerations related to institutional rules, attention dynamics and partisan politics. Empirically, we apply zero-inflated beta regressions on a dataset covering about 1,700 bills adopted from 1995 to 2015 in the Swiss Parliament. Moreover, we consider the government's anticipation strategy to address the problem of observational equivalence affecting analyses of parliament's impact on law-making. Results highlight a reasonably high amendment activity, but with strong variations across bills. MPs change bills more if they are subject to direct democracy, rank high on the parliamentary agenda or if they attract media attention. The influence of the electoral cycle and coalition politics is not confirmed.