The episode described as a Wild West-style "saloon bar brawl" took place in the village of Rutino near Salerno, in southern Italy. It all erupted over the lease on the restaurant, which is owned by the Catholic Church.
The 49-year-old restaurateur said he rushed to the eatery on hearing that the priest and nuns were causing trouble.
He told police that he got into an argument with the priest, who smashed a chair over his head. The nuns followed up by kicking him in the stomach.
Stunned passers-by were shocked to see tables and chairs being hurled around the bar and promptly called the police.
"I came down to try to calm things down but the priest hit me with a chair and I ended up on the floor. Then the two sisters started kicking me, insulting me with unrepeatable words," the unnamed owner said in a statement.
He was taken to hospital with injuries to his neck and bruising to his abdomen.
A lawyer for the clergy disputed his version of events, noting that the nuns had "a combined age of 160."
"This establishment was being occupied illegally," said lawyer Gaetano Di Vietri. "As to the alleged aggression, I would only say that the two nuns have a combined age of about 160. For the rest, it will be up to the magistrate to clear up, but the clergy members deny the allegations."
The priest and nuns belong to a religious order, the Disciples of Santa Teresa and the Baby Jesus, which owns the lease on the premises and reportedly wants the property back.