16 Nonetheless the difficulties of every kind hindering reconciliation increased from year to year. The most serious of these was that the kings of Poland, who at first were regarded as patrons and promoters of the scheme, were now compelled by the fear of their foreign foes and by domestic factions to make ever greater concessions to those, and there were not wanting some, who hated Catholic unity. The result was that in a short time, as the Ruthenian bishops themselves confessed, this holy cause was left with no other protection to rely upon but that of the Roman pontiffs. They for their part supported the Ruthenian Church by affectionate letters, such helps as they could supply, and particularly by means of the Apostolic Nuncio in Poland.
Source: Orientales Omnes Ecclesias (Vatican.va)