Government regulation, such as the pricing of externalities, often raises the unit costs of regulated firms, and its impact on their profits is important to its political economy. We introduce a reduced-form model (“GLM”) that nests existing models of imperfect competition under weaker assumptions. We show how a firm's cost passthrough is a sufficient statistic for the profit impact of regulation. We apply the GLM to carbon pricing for US airlines. We find large inter-firm heterogeneity in pass-through, even for a uniform cost shock. The GLM allows us to sidestep estimation of a consumer demand system, firm markups and conduct parameters. We derive the second-best emissions tax including lobbying a government “for sale”.