(CNN) – Pope Francis has issued new rules restricting the use of the Latin Mass, previously promoted by his predecessor Benedict XVI.

In a letter to Catholic bishops released on Friday, Francis said the restrictions were necessary because the earlier reform had become a source of division between those who preferred Latin Mass and those who adopted the renewed Vatican II cult.

“Taking advantage of an opportunity presented by St. John Paul II and Benedict XVI, it was destined to restore the unity of the body of a church with various cults, to widen gaps, to strengthen differences, and to promote dissent that is harmful to the Church.”

The new law, called Traditions Custodians, requires bishops to recognize the Latin celebration of Mass in their diocese and prohibit it from being celebrated in parish churches.

The law also states that when the mass is celebrated in Latin, the readings must be in the local language, but not in Latin.

Any priest ordained after the New Testament who wishes to celebrate the traditional mass in Latin must obtain formal permission from his bishop, who must obtain permission from the Vatican.

In 2007, Pope Benedict XVI issued the Pontifical Epistle, which expanded access to the Latin Mass and encouraged the clergy to provide it if requested by the faithful.