The article examines the impact of official and unofficial actions of Russian statesmen in supporting the Transcarpathian and Galician Greek Catholics' transitions to Orthodoxy on the growing political tension between the Russian Empire and Austria-Hungary. The authors come to the conclusion that both the transitions of Greek Catholics to Orthodoxy and the policy of the Russian authorities on this issue were extremely painful for the Austro-Hungarian government and undoubtedly played a significant role in unleashing the First World War.