The article deals with the religious situation among the East Slavic immigrants in the United States in the last third of the 19th century. At this time the mass migration overseas from the Eastern regions of Austria-Hungary began. It consisted mainly of Rusyns/Ruthens, Galicians, Lemkos etc. It is noted that most of them were Greek Catholics (Uniates), but they considered their Religion as Russian. In the United States, they, on the one hand, faced rejection by local Roman Catholic hierarchs but, on the other hand, they found themselves in conditions of religious freedom, which were completely new for them. This led to a spontaneous movement for the conversion to Orthodoxy, which started at the beginning of the 1890s and was quite popular among East Slavic immigrants. The paper shows the significance of the religious factor in the process of self-identification of Slavic immigrants. In conclusion, it is stated that, despite the religious schism, a significant part of East Slavic immigrants in the United States continued to feel their historical and/or national unity, to participate in the activities of inter-religious organizations and even to influence their compatriots in their former Homeland.