"Some sisters employed by clergymen get up at dawn to prepare breakfast and only go to bed once dinner has been served, the house cleaned and the laundry washed and ironed," said Sister Marie, who came to Rome from Africa 20 years ago.
Voicing criticism is no simple task for nuns from developing countries, who may have had school fees or medical care for their relatives paid by their religious congregations.
"The sisters feel obliged, bound and so they keep quiet," Marie told the monthly magazine "Women, Church, World" published with the official Vatican daily L'Osservatore Romano.
Pope Francis in 2016 said nuns should speak out against unreasonable work conditions but warned against falling into the "trap of feminism".
Sister Marie vented her frustration in the magazine alongside sisters Paule and Cecile, blasting miserable working conditions and callous treatment from the clergy.
"The sisters do not have a precise timetable as they would in the lay world and their financial reward is unpredictable and often very modest," she said.
Sister Marie said she was particularly irked by clergymen hardly ever inviting the nuns that work for them to eat the dinner they had prepared.
"Is it normal for a clergyman to be served in this way by a clergywoman?" she asked.
"They feel profoundly frustrated but they are afraid of speaking out," she said.
The three nuns speaking out on Friday were not identified by their real names in the magazine.
Sister Paule complained that nuns rarely have a contract with the senior clergymen or parishes they work for, and "therefore get little or no pay at all".
She added that sick nuns are often sent back to their congregations to be replaced by new ones "as if they were interchangeable".
"I have known sisters who worked for a Church institution for 30 years and said that when they got ill none of the priests that they had worked for came to visit them," she said.
Sister Cecile, a teacher who said she worked without a contract, said nuns were perceived as "volunteers that can be disposed of as you wish, which leads to real abuses of power".