New hampshire constitution
Part I – bill of rights
Article 39

No law changing the charter or form of government of a particular city or town shall be enacted by the legislature except to become effective upon the approval of the voters of such city or town upon a referendum to be provided for in said law. The legislature may by general law authorize cities and towns to adopt or amend their charters or forms of government in any way which is not in conflict with general law, provided that such charters or amendments shall become effective only upon the approval of the voters of each such city or town on a referendum.