Whether Puerto Rico may invoke parens patriae standing in federal court on the same basis as a State.
Holding
Yes. Puerto Rico may assert quasi-sovereign interests through a parens patriae action at least as strongly as a State may.
Reasoning
Parens patriae standing does not arise merely because a government chooses to represent particular private citizens. The government must assert an injury to an interest of its own—known as a quasi-sovereign interest—rather than serve as a nominal plaintiff pursuing only private claims.
A quasi-sovereign interest differs from a State's direct sovereign interests, such as enforcing its laws, and from proprietary interests, such as protecting state-owned property. It concerns the government's distinct interest in the well-being of its population and in its status within the federal system.
Although Puerto Rico is a Commonwealth rather than a State, the Court agreed with the parties and lower courts that it is similarly situated to a State for this purpose. Puerto Rico therefore may seek judicial protection for its quasi-sovereign interests against private defendants.