In 2011, in response to the ongoing problem of interstate air pollution, EPA promulgated the Transport Rule to restrict emissions in upwind states in order to achieve attainment of certain national ambient air quality standards in downwind states. State and local governments and industry and labor groups, unhappy with EPA’s process of determining which states would be regulated under the Transport Rule, challenged the rule on the grounds that EPA had exceeded its authority under the Clean Air Act. In 2014, in EPA v. EME Homer City Generation, L.P., the Supreme Court of the United States held that the Transport Rule is a permissible construction of the Good Neighbor Provision of the Clean Air Act. This Comment argues that the Transport Rule, because it permits cost consideration in determining emission reductions for upwind states with no textual authority to do so, is an impermissible interpretation of the Good Neighbor Provision by EPA. The Court’s holding in Homer authorizes EPA to force states to implement any measures it deems cost-effective, even if the measures require states to decrease their emissions by more than their share of pollution.