Pope Leo XIV took the most significant disciplinary action of his young pontificate on Thursday, formally excommunicating the breakaway Society of St. Pius X (SSPX) after the group ignored his personal plea not to consecrate bishops without papal approval. One day after the radical traditionalist fraternity ordained four new bishops in Switzerland in direct violation of canon law, the Vatican’s Dicastery for the Doctrine of the Faith issued a decree declaring the SSPX to be in schism with the Catholic Church. The decree declared that the two bishops who performed the consecrations, along with the four newly ordained bishops, had incurred automatic excommunication under canon law. The Vatican went further still, warning Catholic clergy and lay faithful not to formally adhere to the SSPX’s schism, stating that those who do likewise risk excommunication. In an accompanying explanatory note, the Vatican also reversed pastoral concessions previously granted to the society under Pope Francis, declaring that confessions heard by SSPX priests and marriages performed by them are now invalid. The decision came after Pope Leo made a final personal appeal to the society not to proceed with the illicit ordinations. “In this spirit, and filled with Christian affection, I plead with you and ask you with all my heart: Please turn back,” the pope wrote before the ceremony. The SSPX ignored the warning and proceeded with a five-hour ceremony in Écône, Switzerland, attended by roughly 16,000 worshippers. The confrontation marks the most serious internal crisis of Leo’s pontificate thus far, but it is also the culmination of a dispute stretching back more than half a century. The Society of St. Pius X was founded in 1970 by Archbishop Marcel Lefebvre in opposition to reforms adopted after the Second Vatican Council. While best known for celebrating the Traditional Latin Mass, the society’s objections extend well beyond liturgical preferences. The group has rejected aspects of Vatican II concerning religious liberty, ecumenism, and the Church’s relationship with other faiths, while frequently accusing modern Church leaders of doctrinal error. The conflict first boiled over in 1988 when Lefebvre consecrated four bishops without the permission of Pope John Paul II. The Vatican immediately declared him and the newly ordained bishops excommunicated. Subsequent popes sought reconciliation rather than permanent separation. Pope Benedict XVI lifted the bishops’ excommunications in 2009 as part of an effort to heal the divide, while Pope Francis made extraordinary pastoral concessions by allowing SSPX priests to validly hear confessions and assist at marriages despite the society remaining outside full communion with Rome. Those efforts ultimately failed to bring the fraternity back into the Church. The Vatican noted Thursday that decades of theological dialogue dating back to Pope St. Paul VI had not resulted in reconciliation, and that the SSPX’s latest decision to consecrate bishops without papal approval constituted a definitive schismatic act. The decree also makes clear that the sanctions do not apply broadly to Catholics attached to the Traditional Latin Mass. Rather, they apply to the Society of St. Pius X and those who formally adhere to what the Vatican now describes as its schism. Many traditionalist communities remain in full communion with the Holy See while continuing to celebrate the pre-Vatican II liturgy under the Church’s authority. Even as it imposed the Church’s most severe canonical penalty, the Vatican left open the possibility of reconciliation. The decree states that “the Church, as a caring mother, will welcome with sincere affection and lively solicitude all those who wish to return to full communion.”