Political status of the Cook Islands and Niue
The political status of the Cook Islands and Niue is formally defined as being states in free association within the Realm of New Zealand, which is made up of the Cook Islands, Niue, and New Zealand and its territories, Tokelau and the Ross Dependency. Despite both states acting internationally as independent countries, all Cook Islands and Niue nationals are automatically New Zealand citizens, and while both the Cook Islands and Niue have expressed a desire to become full members of the United Nations, New Zealand has said that they would not support the application without a change in their constitutional relationship, in particular their right to New Zealand citizenship.
Source: Wikipedia — Political status of the Cook Islands and Niue (CC BY-SA 4.0)