International organizations — Immunity — Jurisdictional immunity — Food and Agriculture Organization of the United Nations (“FAO”) — Employment dispute — Head telephonist — Action brought before Italian courts for reinstatement following dismissal — Whether FAO entitled to jurisdictional immunity — FAO-Italy Headquarters Agreement, 1950, Article VIII (Section 16) and Article VII (Section 14) — Scope of immunity of FAO from legal process — Whether application of general rules of customary international law on immunity of international organizations excluded by specific treaty provisions on immunity of FAO — Convention on Privileges and Immunities of Specialized Agencies of the United Nations, 1947, Article IX (Section 31(a)) — Requirement for specialized agencies to make provision for settlement of disputes — Resolution No 71 (1953) adopted by FAO — Express acceptance by FAO of jurisdiction of Administrative Tribunal of the United Nations over employment disputes — Whether excluding jurisdiction of courts of forum State

Treaties — Interpretation — Principles of interpretation — Subsequent practice in the application of the treaty — Vienna Conventions on the Law of Treaties, 1969 and 1986, Article 31(3) — Whether reflecting existing rule of customary international law applicable to international agreements concluded prior to Vienna Conventions — FAO-Italy Headquarters Agreement, 1950 — Interpretation — Relationship to Convention on the Privileges and Immunities of the Specialized Agencies of the United Nations, 1947 — Complementary nature of relationship pursuant to Article XVII (Section 34) of Agreement

Treaties — Conclusion and operation — Constitutional limitations — FAO-Italy Headquarters Agreement, 1950 — Immunity of FAO from claims arising from employment disputes — Acceptance by FAO of jurisdiction of Administrative Tribunal of the United Nations for the settlement of employment disputes — Whether exclusion of jurisdiction of courts of forum State violating Italian Constitution — Right of individuals to judicial protection (Article 24) — Limitations of sovereignty justified in interests of international organizations (Article 11)

Sources of international law — Treaties — Vienna Conventions on the Law of Treaties, 1969 and 1986 — Article 31(3) — Whether declaratory of existing rule of customary international law so as to circumvent non-retroactivity of Treaties under Article 4 — The law of Italy