Church officials in this eastern Indian city say the Vatican has done injustice to Mother Teresa in rushing through her beatification in just six years after her death.
"Many have doubted the haste with which the Vatican expedited the case," Father A.C. Josh, an expert in canon law, told AFP.
Pope John Paul II will on Sunday crown the fastest process yet of beatification in a solemn ceremony in Rome.
It will take the diminutive nun from Calcutta, treated as a living saint during her life because of her humility and service to the most wretched of the poor, within touching distance of full sainthood.
The process leading to the beatification -- the penultimate step to being canonised a saint -- has been the shortest in modern history.
Last year, the Vatican recognized the healing of an Indian Hindu woman, Monica Besra, as a miracle after she had invoked the nun's intercession.
However, doubts persist in medical circles that the disappearance of her stomach tumour could be deemed "miraculous".
Indian rationalists have said it would be a shame if Mother Teresa's elevation to sainthood were based on "lies", saying she deserved to be considered a saint for her work for Calcutta's poor.
"Doubts have been left about the process of the diocesan inquiry as it has already triggered controversy about the miracle attributed to Mother Teresa which paved the way to her beatification," said Father Josh.
"I objected to the speedy process of the inquiry as Mother Teresa's name should not be drawn into further controversy. Her biographers might say it was done so much out of exception which was unnecessary."
Pope John Paul II, one of Mother Teresa's greatest admirers, took the unprecedented step of waiving the normal five-year cooling off period required after death, setting her on a fast-track to sainthood proper. The normally lengthy process began only two years after her death.
Following the beatification on Sunday, a second miracle has to verified by the Vatican before Mother Teresa can be proclaimed a saint.
"When you write things in a hurry, some doubts are left in the whole process of inquiry into the life, virtue and sanctity of Mother Teresa. When asked about the miracle attributed to Mother Teresa, I suggested that those who objected to it must be given a chance to testify it," said Josh.
"Medical reports of the healing of Besra through the blessings of Mother Teresa were not published. It lacks thoroughness. Obviously some doubts are left."
The Calcutta priest said the Vatican should exhume Mother Teresa's body and put it on display.
"It is a customary process. I hope the body of Mother Teresa will go on display at a later stage as a lot of people want to see it," said Father Josh.
"People are saying Pope John Paul II was close to Mother Teresa so he put her case on the fast-track for sainthood arousing some suspicion. It is also a personal wish of Pope John Paul II to beatify Mother Teresa... a crowning point in his time."
A salesian priest, Father Robin Gomes said the Vatican in its haste to beatify the Calcutta nun had not done her enough justice.
"The Vatican should have waited for the five years after the death of Mother Teresa before starting the diocesan inquiry. The slower the process the better for the church as it would have given it opportunities to justify the cause of sainthood," said Gomes.
"It would have been wiser had the Vatican been a little more serious in the case of Mother Teresa," he added.