The Moscow Patriarchate did not wait for the Tomos to be issued before acting. In October 2018, once the Ecumenical Patriarchate announced its intention to proceed toward granting Ukrainian autocephaly, the Russian Orthodox Church broke eucharistic communion with the Ecumenical Patriarchate entirely, a rupture that as of this writing remains unresolved. Moscow's core argument is twofold: that only a pan-Orthodox council, not a unilateral act by Constantinople, has the authority to grant autocephaly to a church, and that Ukraine has been canonically Russian ecclesiastical territory since the Kyiv Metropolia's transfer to Moscow's jurisdiction in 1686, making any grant of independence by Constantinople an act of trespass on another church's territory rather than a legitimate exercise of primacy.
The dispute did not stay confined to the two patriarchates directly involved. Other autocephalous Orthodox churches split in their own response, with the Church of Greece, the Patriarchate of Alexandria, and the Church of Cyprus each extending some form of recognition to the Orthodox Church of Ukraine at various points, while other autocephalous churches withheld recognition entirely, leaving Ukrainian Orthodox ecclesiastical status one of the least settled jurisdictional questions anywhere in contemporary world Orthodoxy.