Rome (CNN)A major change may be coming to the Catholic Church from an unlikely place: the Amazon.
This Sunday kicks off a three-week meeting of bishops at the Vatican to discuss, among other things, ordaining some married men as priests to help alleviate a shortage of Catholic clergy in the nine countries of the Amazon region.
Pope Francis convened the meeting, called a synod, to discuss environmental and religious issues in the Amazon and give special attention to the needs of indigenous communities there.
The region includes parts of Brazil, Peru, Ecuador, Colombia, Venezuela, Guyana, Surinam and French Guiana. The Vatican has invited 184 bishops and priests from those countries and from around the world to participate in the synod and vote on measures. Thirty-five women, mostly religious sisters and nuns, have been invited but will not have voting rights.
There will be 17 representatives of the Amazon's indigenous populations, including 9 women, will attend as well.
But before it even begins, the synod has become the center of controversy for both conservatives and liberals.
Ordaining married men
The Pope told bishops from the region to "be bold" in their proposals for the meeting and Bishop Erwin Krautler, the church's Secretary for the Commission on the Pan-Amazon Region, says he hopes the meeting will address not only ordaining married men, but women too.
"We don't just speak about men because it's exclusionary," Krautler told CNN. "We also want to include women."
The possibility that centuries of Catholic tradition of a celibate priesthood might be overturned has caused conservative outrage.
American Cardinal Raymond Burke and Bishop Athanasius Schneider of Kazakhstan have warned of "heresy" and called for "a crusade of prayer and fasting," for forty days throughout the synod.
Earlier this week, some 200 Catholics, calling themselves a "spiritual army" stood in formation, rosaries in hand, under the statue of St. Michael the Archangel near the Vatican, to pray for the synod.
"It really is, at the end of the day, a battle of angels," said Michael Voris, founder of Church Militant, a far-right Catholic group based in the US. "It's a battle of the good angels and a battle of the demons.
The battle over ordaining married men may not turn out to be as contentious as some fear, however.
Canadian Cardinal Marc Ouellet, who heads the Vatican's powerful office for bishops and will be voting in the synod, said he is leaning against the proposal.
"I am skeptical, and I think I am not the only one," Ouellet said at a press conference in Rome on Wednesday.
"There is someone above me who is even more skeptical who has authorized the debate and that's OK," he said, in an apparent reference to Pope Francis.
The Pope decides
It is the Pope who will ultimately decide what, if any, changes will be made to the current church practice of celibate priests, based on the recommendations from the synod.
Francis has said that he is open to studying the possibility of ordaining married men, called "viri probati" for remote areas in the Amazon that are without priests.
The proposals would not affect the current practice of mandatory celibacy for Catholic priests, which the Pope has said will not change.
Women's vote
The drumbeat of discord around this synod, however, is not just coming from conservatives.
Nuns and activists from several women's organizations have taken to the streets outside the Vatican, protesting a synod rule that does not allow women to vote.
Of some 250 participants at the synod, 35 are women. Most of the women are invited as "listeners." Only the 184 men will be voting on the proposals.
On Thursday, activists from the groups Future Church, Women's Ordination Conference and Voices of Faith projected a light sign, "Votes For Catholic Women," on the doors of the Vatican's powerful doctrinal office, the Congregation for the Doctrine of the Faith.
Nuns in black habits, from convents in the Philippines, Germany and Switzerland, joined a prayer vigil outside the Vatican offices, holding signs demanding the right to vote.
"I am here because my sisters are engaged in the Amazon and they need to be engaged in this synod in a more vibrant form," Sister Simone Campbell, an American nun and executive director of NETWORK, told journalists at a press conference in Rome on Thursday.
Organizers of the synod have defended the rules which restrict voting rights to men saying that any change in the norms would be up to Pope Francis.
"I think we must stick with the norms and the interpretation of these norms rests with the Holy Father," said Cardinal Lorenzo Baldisseri, secretary general of the synod, at a press conference on Thursday.
How the synod works
The synod is conducted behind closed doors. Voting members each have an opportunity to speak, usually for about 10 minutes each, on topics related to the agenda.
The agenda, called by its Latin name the Instrumentum Laboris, or working document, consists of 147 points, which are condensed into a final document and voted on at the end of the Synod by a "yea" or "nay" vote.
Point 129 of the Instrumentum Laboris contains the suggestion that, "the possibility of priestly ordination be studied for older people, preferably indigenous, respected and accepted by their community, even if they have an existing and stable family, in order to ensure availability of the Sacraments that accompany and sustain the Christian life."
Included in point 129 is the question of the role of women.
"Identify the type of official ministry that can be conferred on women, taking into account the central role they play today in the Church in the Amazon."
A 'green' synod
The agenda includes points on appreciating and protecting indigenous rituals and herbal medicine, especially when exploited by pharmaceutical companies; regulating industry which pollutes the environment and takes land from indigenous people; protecting the rainforests of the Amazon and assisting the poor and women.
Highlighting with the ecological theme of the meeting, the Vatican announced that it will introduce some environmentally friendly measures for the event, including biodegradable drinking cups, natural-fiber tote bags and recycled paper.
