A rebel group of traditionalist Catholics has gone ahead with the ordination of four bishops without the approval of Pope Leo XIV, in the first major challenge to his papal authority.

The Society of Saint Pius X, a group that rejects reforms made by the Catholic Church in recent decades, conducted the ordinations Wednesday in a ceremony attended by thousands in Écône, Switzerland.

According to church law the four bishops being ordained, and those bishops involved in adminstering the rite, are automatically excommunicated, or excluded from the sacraments of the church.

Vatican News reported that about 15,000 people attended the ordination ceremony, which was conducted in a white marquee and livestreamed in six languages on the society’s website.

The Vatican has not yet formally responded to the news.

In an 11th-hour appeal to the group Monday, Leo had warned that the ordinations would be a “schismatic” act and a “sin of extreme gravity.”

In Catholic teaching, the link, or communion, between bishops and the pope is a cornerstone of the church’s unity. Since his election, Pope Leo has made fostering church unity a focus, but the society’s decision to proceed with the consecration of bishops without the pontiff’s consent will be viewed as a serious violation of church law.

The society, known as the SSPX, has an active presence in the United States, with a headquarters in Missouri and a seminary for training priests in Dillwyn, Virginia. One of the bishops newly ordained on Wednesday is Father Michael Goldade, who leads that seminary.

The group was founded in 1970 in Switzerland by Archbishop Marcel Lefebvre, a French prelate, but five years later was officially suppressed by the Bishop of Fribourg. In 1988 the group ordained four bishops without papal approval, which led to their excommunication.

At the heart of the splintering from the mainstream church was Lefebvre and his followers’ opposition to church reforms introduced in the 1960s by the Second Vatican Council.

The “Lefebvrists” do not accept what the council taught on religious freedom, on ecumenism (teaching on other Christian denominations and religions) and reforms to Catholic worship. One of the major reforms at the council was a condemnation of all forms of antisemitism.

Lefebvrists insist they need to ordain bishops without approval because the Catholic Church is in a “state of emergency” due to what they see as the introduction of liberal and “modernist” ideas. The group believes it must prioritize “the salvation of souls” and in recent days issued a 28-page “profession of Catholic faith” to “enlighten souls in the face of modern errors.”

While the SSPX numbers around 700 priests and 600,000 followers worldwide – relatively small, given the Roman Catholic Church has 1.4 billion members and around 400,000 priests – the threat to unity is being taken seriously by the pope.

Cardinal Blase Cupich of Chicago, who is a close ally of Leo, told CNN ahead of the ordinations that “the danger” was “the setting up of a parallel structure within the ecclesial body of the church.”

He said the pope had issued numerous invitations for the society to reconsider its plans.

“They are a small group, however they do misuse the rites of the church when it comes to having bishops ordained,” the cardinal said. “He (Leo) is very serious about the issue and that’s why he has had multiple interventions.”

In recent decades, various popes have sought to reconcile with the group and in 2009 Pope Benedict XVI lifted the excommunications of the four bishops ordained in 1988. However, one of those bishops, Richard Williamson, was later found to have falsely claimed the Nazis did not use gas chambers in the Holocaust and would later be prosecuted and convicted by a German court. He was subsequently expelled from the society.

A website details four days of events around the latest ordinations, which includes the offer of a 75 Swiss Franc souvenir box of four bottles of wine.

In remarks to journalists on June 16, the pope said he was open to dialog but was also aware of the limits as regarded the planned ordinations. “If they make that choice, I am sorry, but we must move forward,” he said. (CNN)