basis for holding, on the merits, that the FDA's refusal to grant the relief requested was within its discretion.
First, respondents on summary judgment neither offered nor attempted to offer any evidence that the reasons for the FDA's refusal to act were other than the reasons stated by the agency. Second, as the Court correctly concludes, the FDCA is not a mandatory statute that requires the FDA to prosecute all violations of the Act. Thus, the FDA clearly has significant discretion to choose which alleged violations of the Act to prosecute. Third, the basis on which the agency chose to exercise this discretion—that other problems were viewed as more pressing—generally will be enough to pass muster. Certainly it is enough to do so here, where the number of people currently affected by the alleged misbranding is around 200, and where the drugs are integral elements in a regulatory scheme over which the States exercise pervasive and direct control.
When a statute does not mandate full enforcement, I agree with the Court that an agency is generally "far better equipped than the courts to deal with the many variables involved in the proper ordering of its priorities." Ante, at 831–832. As long as the agency is choosing how to allocate finite enforcement resources, the agency's choice will be entitled to substantial deference, for the choice among valid alternative enforcement policies is precisely the sort of choice over which agencies generally have been left substantial discretion by their enabling statutes. On the merits, then, a decision not to enforce that is based on valid resource-allocation decisions will generally not be "arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law," 5 U. S. C. § 706(2)(A). The decision in this case is no exception to this principle.
The Court, however, is not content to rest on this ground. Instead, the Court transforms the arguments for deferential review on the merits into the wholly different notion that "enforcement" decisions are presumptively unreviewable
