Under Habsburg rule, Roman Catholics dominated Transylvania's more numerous Protestants, and Vienna mounted a campaign to convert the region to Catholicism. The imperial army delivered many Protestant churches to Catholic hands, and anyone who broke from the Catholic church was liable to receive a public flogging. The Habsburgs also attempted to persuade Orthodox clergymen to join the Uniate Church, which retained Orthodox rituals and customs but accepted four key points of Catholic doctrine and acknowledged papal authority. Jesuits dispatched to Transylvania promised Orthodox clergymen heightened social status, exemption from serfdom, and material benefits. In 1699 and 1701, Emperor Leopold I decreed Transylvania's Orthodox Church to be one with the Roman Catholic Church; the Habsburgs, however, never intended to make the Uniate Church a "received" religion and did not enforce portions of Leopold's decrees that gave Uniate clergymen the same rights as Catholic priests. Despite an Orthodox synod's acceptance of union, many Orthodox clergy and faithful rejected it.

In 1711, having suppressed an eight-year rebellion of Hungarian nobles and serfs, the empire consolidated its hold on Transylvania, and within several decades the Uniate Church proved a seminal force in the rise of Romanian nationalism. Uniate clergymen had influence in Vienna; and Uniate priests schooled in Rome and Vienna acquainted the Romanians with Western ideas, wrote histories tracing their Daco-Roman origins, adapted the Latin alphabet to the Romanian language, and published Romanian grammars and prayer books. The Uniate Church's seat at Blaj, in southern Transylvania, became a center of Romanian culture.

The Romanians' struggle for equality in Transylvania found its first formidable advocate in a Uniate bishop, Inocentiu Micu Klein, who, with imperial backing, became a baron and a member of the Transylvanian Diet. From 1729 to 1744 Klein submitted petitions to Vienna on the Romanians' behalf and stubbornly took the floor of Transylvania's Diet to declare that Romanians were the inferiors of no other Transylvanian people, that they contributed more taxes and soldiers to the state than any of Transylvania's "nations," and that only enmity and outdated privileges caused their political exclusion and economic exploitation. Klein fought to gain Uniate clergymen the same rights as Catholic priests, reduce feudal obligations, restore expropriated land to Romanian peasants, and bar feudal lords from depriving Romanian children of an education. The bishop's words fell on deaf ears in Vienna; and Hungarian, German, and Szekler deputies, jealously clinging to their noble privileges, openly mocked the bishop and snarled that the Romanians were to the Transylvanian body politic what "moths are to clothing." Klein eventually fled to Rome where his appeals to the pope proved fruitless. He died in a Roman monastery in 1768. Klein's struggle, however, stirred both Uniate and Orthodox Romanians to demand equal standing. In 1762 an imperial decree established an organization for Transylvania's Orthodox community, but the empire still denied Orthodoxy equality even with the Uniate Church.

Data as of July 1989