Mexican drug cartels have crossed a disturbing moral boundary: They are now deliberately murdering Catholic clergy, according to CNN.

The killing last weekend of a Catholic priest and two seminary students in southwest Mexico marked the first time that drug cartel hit men have purposefully targeted a clergyman, said Manuel Corral, public relations secretary for Mexico’s Council of Bishops.

The Rev. Habacuc Hernandez Benitez, 39, was gunned down as he traveled in a vehicle in the town of Arcelia in the state of Guerrero, together with two seminary students, Eduardo Oregon Benitez, 19, and Silvestre Gonzalez Cambron, 21.

“In this case the drug traffickers followed them and ambushed them,” said Corral, who declined to name which cartel is suspected behind the incident.

CNN reports that at least seven priests have been murdered in Mexico since 2005, but this weekend’s killings are the first where it’s clear clergy have been deliberately killed by cartel hit men.

The clergy has not been spared from the spike in drug-related violence that has afflicted regions of Mexico, Corral said.

“The threats are not new,” he said. “As drug trafficking continued to grow, from about 2004 on, the priests continued to denounce it, and they themselves were threatened.”

In April, the archbishop of the northern state of Durango raised fears of attacks on the clergy after he said that Mexico’s most wanted man, Sinaloa cartel boss Joaquin “El Chapo” Guzman, lives in a Durango town and that “everybody knows it except the authorities.” The comment, which was made in private conversation, stirred fears of retaliation and the archbishop backed off his statement after it quickly spread.

Of the 15,000 priests in Mexico, Corral estimated that 1,000 had been threatened in some form, and that 300 priests have been threatened directly. Those direct threats — usually in the form of “shut up, or we’ll shut you up” — have come from intermediaries for organized crime or anonymously, Corral said.

The threats against the clergy have been serious enough that in some 20 cases, priests in Mexico were transferred to other parishes out of regard for their safety, he said.