When do criminal organizations use violence to influence political outcomes? Using an asymmetric information model, I show that criminal groups use violence when other channels of influence, namely bribes, are no longer available to them. I test the model predictions in the context of an electoral reform in Mexico that increased politicians’ cost of accepting bribes. I use confidential administrative reports of suspicious financial transactions in retail banking to measure bribes and an original dataset of attacks on politicians to measure violence. Results from a difference-in-differences design indicate that the reform differentially decreased the number of suspicious financial reports by 4 percentage points (∼650 fewer reports) and increased the number of attacks by 2 percentage points (∼44 more attacks) in places with the presence of drug trafficking organizations. Consistent with the model, additional evidence suggests that (1) criminal organizations resort to violence when they fail to reach an agreement with politicians, and (2) the effects of the reform are driven by municipalities where politicians have tighter campaign spending limits and less information about the criminal group(s).These findings have implications for our understanding of local governance and call for attention to the design and implementation of transparency-enhancing electoral reforms.