A Romanian baby died after a christening ceremony in which babies are immersed in holy water three times.
The 6-week-old baby was taken to a cardiac arrest hospital on Monday and died a few hours later, an autopsy reported a liquid in his lungs, Agence France-Presse reported.
The tragedy pressured the Orthodox Church to change the rules of baptism.
Prosecutors have opened an investigation into the murder of the priest in the city of Suceava.
“The death of a newborn baby because of this practice is a huge tragedy,” said a message with an online petition to make changes to the ritual. “That risk must be ruled out for the joy of baptism to triumph.”
By Thursday evening, the petition had gathered more than 56,000 signatures, according to AFP.
One person online denounced the “brutality” of the ritual and another criticized the “stubbornness of those who think it is God’s will” to keep it.
Local media reported on several similar incidents in recent years.
Church spokesman Vasile Banescu said priests could pour some water over a baby’s forehead instead of a full dive.
But Archbishop Theodosius, leader of the traditional wing of the Church, stood firm and insisted that the whole ritual would not change.
In Romania, where more than 80 percent of the population is Orthodox, the Church is one of the most trusted institutions, according to recent opinion polls.