International organizations — Immunity — Jurisdictional immunity — Whether limited to acts performed iure imperii — Intergovernmental Committee for European Migration-Italy Headquarters Agreement, 1952 — Convention on the Privileges and Immunities of the Specialized Agencies of the United Nations, 1947 — National of receiving State employed as secretary — Contract of employment — Claim for severance pay — Whether ICEM entitled to immunity from jurisdiction of municipal courts — Nature of employment relationship — Criteria for determining which employment relationships with international organizations covered by jurisdictional immunity — Whether any obligation for international organizations to provide machinery for settlement of employment disputes — The law of Italy