Sister Lavinia Byrne, 52, has been a target of the doctrinal watchdog agency since 1993 when she published a book, "Woman at the Altar," examining the role of women in the church and arguing for the ordination of women.
The book was condemned by the CDF, and in the United States 1,300 copies were withdrawn from sale.
Later, according to Byrne, the CDF put pressure on her to make a public statement supporting "Humanae Vitae," Paul VI's 1968 encyclical condemning artificial means of birth control, and Pope John Paul II's ruling that only men could be ordained to the priesthood.
She said she could do neither with a clear conscience and that is why she was leaving the Institute of the Blessed Virgin Mary -- the "English Ladies" religious order founded in 1609 by Mary Ward and briefly suppressed by Pope Urban VIII in 1631.
"My quarrel is not with the community here or the Catholic Church in this country, but with the CDF in Rome," she said. "They are using techniques that seem to belong to another age. They are behaving like the Inquisition. I feel bullied."