摘要：How free should the federal government be, not only to preempt state regulatory law, but also to choose itself to adopt no law on point? Such instances of “null preemption” have been historically rare, but now are occurring with greater frequency. Consider that the Environmental Protection Agency (EPA) refused to allow states to impose standards governing motor vehicle tailpipe greenhouse-gas emissions, and also argued that it could not, or alternatively would not, issue any federal regulations. Further, though the Supreme Court rejected the EPA's arguments, two years have since passed with no EPA action. The regulatory voids resulting from such instances of “null preemption” are rarely normatively justified. Even if states lack a normative justification for regulating, still the structure of the federal system means that null preemption offends states' sovereign prerogative to protect their citizens. Moreover, it is far more likely, not that the states lack any normative justification, but that there is a normative dispute between federal and state government over the propriety of regulation. Only rarely—such as when the federal government seeks to avoid interstate externalities and the cost of national regulation outweighs its benefit—will null preemption be justified. Null preemption should accordingly be limited. Congress can statutorily limit federal regulators' freedom to engage in null preemption. Courts should react skeptically to assertions of null preemption, especially where regulators make such assertions without indication of supporting congressional intent.
关键词：United States. Environmental Protection Agency; Cooperative federalism; Exclusive & concurrent legislative powers; Environmental law
