French priest Father Jacques Lacroix, 89, has been forced to retire after video emerged of him angrily slapping a child.
The video was uploaded to the internet on Thursday (NZ time) after the events took place at the Collegiate Church in Champeaux, France, last Sunday, the Daily Mail reports.
"I'm going to put water on the forehead, and after I'll embrace the little man, because he will have become a little Christian," Fr Lacroix told the parents.
But the baby wouldn't stop crying, so Fr Lacroix grabbed his head and said, "Stop crying, calm down."
The anxious parents appeared to want him to hand the baby back, but he gripped tighter before slapping the baby on the cheek.
The boy's father tried to take the infant, but Fr Lacroix pulled the baby's head towards his own, and said: "You have to calm down, you have to calm down."
Eventually Fr Lacroix relented, the man telling him, "no, no, no". The baby cried the whole time.
Fr Lacroix has denied the slap was too severe, saying he was just trying to calm the baby as it wouldn't stop crying.
"The child was screaming a lot and I had to turn his head to pour water over it," he told France Info Radio.
"I told him to 'calm down, calm down' but he was not calming down. I tried to hold him close. I just wanted him to calm down."
He later said the baptism was his last one ever.
Local Bishop Jean-Yves said immediate measures had been taken to suspend Fr Lacroix from any future marriage and baptism celebrations.
The bishop blamed the incident on Fr Lacroix being old and tired.
"[It was a] loss of coolness that can be explained but not excused," he said.