On June 21, 2010, the Supreme Court decided Monsanto Co. v. Geertson Seed Farms, No. 09-475, holding that a district court abused its discretion when it permanently enjoined the partial deregulation of genetically engineered alfalfa seed and its planting anywhere in the United States until the Agriculture Department complied with the National Environmental Policy Act (NEPA) and completed an environmental impact study to determine the environmental impact of such seed.

The Plant Protection Act permits the Department of Agriculture to issue regulations to prevent the introduction and dissemination of "plant pests" in the United States. Regulations pursuant to that authority presume all genetically engineered plants to be "plant pests" unless the Department determines otherwise. In making this determination, the Department must comply with NEPA, which requires a federal agency to prepare a detailed environmental impact statement (EIS) before taking any major action "significantly affecting the quality of the human environment." An EIS is not required if the agency determines, based on a shorter environmental assessment (EA), that the proposed action will not have a significant environmental impact.

The Department approved the unconditional deregulation from "plant pest" regulation of Monsanto's Roundup Ready Alfalfa seed (RRA), which is genetically engineered to tolerate Monsanto's Roundup herbicide. The Department did not conduct a full EIS before issuing this decision, based on its EA determining that deregulation would not have any significant adverse impact on the environment. A number of growers of conventional alfalfa and several environmental groups sued to overturn this decision. The district court held that the Department had violated NEPA by failing to conduct a full EIS before deregulating RRA, and it issued an injunction enjoining any deregulation, in whole or in part, or any planting of RAA in the United States until an EIS was completed. Monsanto and the federal government appealed, not disputing the finding that the Department had failed to comply with NEPA but challenging the scope of the injunction. The Ninth Circuit affirmed.

The Supreme Court reversed. It first held that all parties had standing—Monsanto because the injunction prohibited them from selling or licensing RRA to prospective customers until the EIS was completed, and the plaintiffs because the district court found there was a reasonable probability that their conventional alfalfa crops would be infected with the genetically engineered gene if RRA were completely deregulated. Because none of the parties disputed the district court's finding that the Department had violated NEPA, the Court assumed without deciding that the district court acted properly in vacating the Department's deregulation decision. But it held that the court had abused its discretion by granting an overly broad injunction. The Court noted that the mere existence of a NEPA violation does not create a presumption that injunctive relief is available or that such relief should always be granted. A party seeking relief under NEPA must satisfy the traditional four-factor test for issuance of an injunction—irreparable harm, inadequacy of legal remedies, a balance of hardships favoring the moving party, and the absence of injury to the public interest if an injunction were issued.

Here, the Court held, none of these factors supported the prohibition against partial deregulation pending completion of the EIS. In particular, the plaintiffs will not suffer irreparable harm if the Department is allowed to proceed with partial deregulation, because they can file a new lawsuit if they believe a partial deregulation order also violates NEPA. Indeed, whether a partial deregulation will cause any injury at all will depend on the scope and terms of the deregulation order. But the injunction here is so broad that it essentially preempts the Department's right to decide, in the first instance, whether a limited deregulation would pose an appreciable risk of environmental harm. For similar reasons, the district court also erred in entering a nationwide order against any planting of RRA until the EIS was completed, regardless of the possibility of a partial deregulation order.

Justice Alito delivered the opinion of the Court, in which Chief Justice Roberts and Justices Scalia, Kennedy, Thomas, Ginsburg, and Sotomayor joined. Justice Stevens filed a dissenting opinion. Justice Breyer took no part in the decision of the case.