This case involves the exception for "rights in immovable property situated in the United States."

Thus, a suit to declare the validity of a tax lien inquestionably places "rights in immovable property" in issue.

A special mortgage in immovable property refers to specific limited real rights in immovable property to secure payment of a debt.

The Second Circuit agreed with the district court, adding that the tax obligations owed by India and Mongolia qualified as "rights in immovable property."

New York is invoking the "immovable property" exception, which provides jurisdiction over cases in which "rights in immovable property situated in the United States are in issue."

The district court disagreed, reasoning that the FSIA did not exempt foreign governments from suits in which "rights in immovable property situated in the United States are in issue."

New York, in turn, cited the "immovable property" exception, under which foreign governments are not immune in a case in which "rights in immovable property situated in the United States are in issue."

"A tax lien thus inhibits one of the quintessential rights of property ownership - the right to convey," Justice Thomas said, adding, "It is therefore plain that a suit to establish the validity of a lien implicates 'rights in immovable property.' "