This case concerns a proposed housing development whose construction was blocked by the Interior Department due to claims that the development would disrupt the habitat of the Arroyo Southwestern toad, an amphibian protected by the Endangered Species Act. The developers challenged this government intervention, claiming that the government’s actions constituted an unlawful “taking.” Cato’s brief, filed jointly with the Pacific Legal Foundation, argues that the ESA, as applied to non-commercial species, lacks a substantial relation to interstate commerce. Throughout its history, the Court has never upheld a Commerce Clause regulation of an activity that was not substantially economic in nature, so the federal government action was an illegitimate intervention into intrastate, noncommercial activities. Indeed, because of these questionable federal interventions, the brief disputes the constitutionality of the ESA itself.