(Bishop Bernard Fellay meets the faithful after an ordination ceremony in Econe, southwest Switzerland, June 29, 2009. REUTERS/Denis Balibouse)

The Vatican on Friday told an ultra-traditionalist Roman Catholic splinter group they must accept non-negotiable doctrinal principles within a month or risk a painful break with Rome that would have “incalculable” consequences.

The ultimatum was issued after a two-hour meeting between Swiss-born Bishop Bernard Fellay, leader of the dissident Society of Saint Pius X (SSPX) and U.S. Cardinal William Levada, head of the Vatican’s doctrinal department.

Levada told Fellay the group’s response after years of negotiations was still insufficient to overcome doctrinal problems at the root of the split with Rome.

The SSPX, which rejects reforms made at the historic 1962 Second Vatican Council, defied Rome in 1988 by illegally consecrating four bishops, triggering their excommunication by the late Pope John Paul.