Pope Benedict's expected revival of the old Latin mass has provoked protests from Roman Catholic clergy in France, a major centre of the traditionalist schism the Pontiff hopes to overcome with the gesture.
Five bishops and 30 priests - a considerable number in a church normally wary of open dissent - have expressed grave concern about making this concession to ultra-conservatives who reject the reforms of the Second Vatican Council (1962-1965).
Unswerving loyalty to the old Latin, or Tridentine mass, often goes hand in hand with a rejection of the Vatican II reforms, which opened the church to respect for and co-operating with other faiths and switched to a modern mass conducted in local languages.
The protests printed in the Catholic press highlighted serious issues the Vatican faces if, as church sources have reported, it announces soon that priests are free to say the vintage mass as an alternative to the modern liturgy.
Demand for a return the Tridentine mass - an austere ceremony in which the priest prays in Latin with his back to a silent congregation - is minimal among the world's 1.1 billion Catholics.
In the modern mass, the priest faces the faithful, who pray and sing in active participation with him. "This could create grave difficulties, especially for those who have remained loyal to Vatican II," Toulouse Bishop Robert Le Gall told the Catholic daily La Croix.
In an open letter, 30 young priests said Benedict, 79, should encourage them "to work in the world as it is ... rather than plunge us back into the liturgical life of another age".
Dating back to 1570, the Tridentine mass was dropped in the 1960s and can now be said only with a bishop's special permission. But the Society of Saint Pius X (SSPX), a Swiss-based group launched by the late French Archbishop Marcel Lefebvre to oppose 1960s reforms, has demanded a blanket permission, or indult, for the Tridentine mass as a condition for its return to the church.
SSPX leader Bishop Bernard Fellay and other leaders were excommunicated in 1988.
Fellay says the Vatican looks set to grant the indult soon to take the SSPX back into the church.
But he insists his million-strong movement, many in France, would continue to contest Vatican II reforms from inside the church, creating a loyal opposition keen to steer it back to earlier practices. The Vatican has already provoked protest in Bordeaux by readmitting five SSPX priests who performed a Tridentine mass in a church they occupied there.
Cardinal Jean-Pierre Ricard, Bordeaux archbishop and head of the French Bishops' Conference, has urged French Catholics to welcome rebel priests who return to the church.
"We can be charitable and welcoming but we also have to be honest," Besancon Bishop Andre Lacrampe told the daily L'Est Republicain. "I'm not ready to receive them because one cannot erase Vatican II with a stroke of a pen."
"There are very deep and painful theological reasons behind this schism," Angouleme Bishop Claude Dagens told the Catholic weekly La Vie. "You can't pretend that Archbishop Lefebvre's break with the church was only caused by the liturgy."
Lille Archbishop Gerard Defois said some SSPX faithful were linked to far-right political movements and noted in a statement that some had "resorted to violent means to occupy churches".