Related Rule
Belgium
Practice Relating to Rule 69. Loss of Inviolability of Parlementaires
Belgium’s Teaching Manual for Officers (1994) states: “The search for information, the fact of provoking or committing an act of treason under the cover of [a parlementaire’s] mission induces the loss of his rights.” 
Belgium, Droit de la Guerre, Manuel d’Instruction pour Officiers, Etat-Major Général, Division Opérations, 1994, Part I, Title II, p. 25.