The federalism structure of the US government requires active cooperation from state governments to successfully enforce federal regulations and this is particularly important for environmental regulations. State governments provide resources and local information to the Environmental Protection Agency (EPA) which can be very valuable when it comes to civil litigations. What explains state governments' participation in lawsuits against private firms that are accused of violating major environmental statutes? We argue that political connections that firms have with state politicians affect a state government’s decision to join the litigation process. To empirically test our argument, we construct a novel dataset on the EPA's civil cases and settlements for the period 1998-2021. For 782 cases, we have rich information on the defendants as well as the state agencies that were involved in the case. We show that state environmental agencies are less likely to join the EPA in court when the defendant firms contributed to Republican state legislators in the previous election cycle, but we do not find the same pattern when firms have political connections with Democratic legislators. We also show that state involvement in litigation is associated with higher penalties as well as more environmental provisions in the judicial outcomes. Our paper highlights how state politics can be an avenue for special interest groups to exert influence to change the outcome of federal regulations.