The NOx State Implementation Plan Call was designed to facilitate cost effective reductions of nitrogen oxides emissions from large stationary sources (primarily electricity generators) through the introduction of an emissions trading program. I investigate the relationship between economic regulation and firms' long-run response to the incentives created by this emissions trading program. I estimate a discrete choice model of the firm's compliance decision, controlling for unit-level variation in compliance costs and using exogenous variation in state-level electricity industry restructuring activity to identify an e¤ect of electricity market regulation on generators' environmental compliance strategy choices. I present evidence that differences in economic regulation across states have resulted in a disproportionate amount of the mandated emissions reductions occurring in more regulated electricity markets. Unfortunately, these are the areas least in need of pollution control.