The acquired rights doctrine limits the ability of an international organisation (io) to unilaterally amend a staff member’s conditions of employment to his or her detriment. The leading international administrative tribunals, especially the Administrative Tribunal of the International Labour Organisation or the ILOAT refined and developed the doctrine’s meaning and scope over decades. There has been a general consensus that the acquired rights doctrine protects a staff member’s essential terms of employment both retrospectively and prospectively. However, in its recent jurisprudence, the United Nations Appeals Tribunal or the UNAT has rendered the acquired rights doctrine with little work to do by reducing it to the principle of non- retroactivity. As a result, the consensus as to the doctrine’s core meaning is now undermined. International civil servants having access to the ILOAT are much better protected from unilateral adverse amendments to their conditions of employment when compared to those international public officials whose organisations have subscribed to the jurisdiction of the UNAT. This is an unwelcome development for the content of substantive protections is now more dependent on the tribunal approach, as opposed to a coherent development of the law.