The article analyses the problem of forced passportization of Ukrainian citizens in the temporarily occupied territories of Ukraine by the Russian occupation authorities during Russia’s armed aggression against Ukraine. This process began as early as the period of the illegal occupation of Crimea and its scale significantly increased with the beginning of the full-scale invasion on February 24, 2022. It is stressed that the forcing of Ukrainians to obtain Russian citizenship is carried out as part of the Russian authorities’ policy. In this context, we analyse the latest legislation of the Russian Federation which relates to the procedure for granting Russian citizenship by the Russian occupation authorities. Examples of forcing Ukrainians living in the occupied territories to obtain citizenship of the Russian Federation through intimidation, threats, and deprivation of basic human rights and freedoms are cited. Forced passportization in the occupied territories of Ukraine, carried out by the Russian authorities, is a violation of the International Humanitarian Law, in particular Article 4 of the IV Geneva Convention of 1949 “On the Protection of the Civilian Persons in the time of war” and Article 4 of the IV Hague Convention of 1907, which prohibits forcing the inhabitants to swear allegiance to the occupying power. It has been established that in contemporary international law, coercion to obtain citizenship of the occupying power does not constitute an independent component of a war crime. It is concluded that such violations of International Humanitarian Law may constitute a war crime and it indicates the need for the criminalization of forced passportization by amending the Rome Statute of the International Criminal Court. It is proposed to constitute a new war crime by adding to Paragraph 2 (b) of Article 8 of the Statute of the International Criminal Court a new war crime: forcing the inhabitants of the occupied territories to obtain citizenship of the occupying state.