Calls be Pope Benedict XVI to defend the traditional family and a bill that would give legal recognition to unmarried couples, including homosexual ones, boosted debates that have split Italy. Tens of thousand of people plan to gather Saturday for the protest.
The legislation, which awaits parliamentary approval, has underscored long-standing tensions in the largely Roman Catholic country between a desire to hold on to church-sanctioned traditions and a push toward further secularization.
Organizers of Saturday's "Family Day" demonstration include lay Catholic groups and family associations. While the demonstration has been endorsed by Italian bishops, neither the Vatican nor the Italian bishops' conference is formally behind it.
"Family belongs to believers and nonbelievers alike," said Gaetano Quagliariello, a center-right senator who helped organize the event. "Family has to do with culture and civilization."
Organizers said they are hoping for a turnout of 100,000, but recent Italian reports said the number of people attending the rally at the massive St. John Lateran piazza could be several times that.
The bill at the heart of the controversy was passed by Premier Romano Prodi's center-left Cabinet in February, spurring tensions in a coalition that includes both hard-line leftists and Christian Democrats.
The proposed legislation stops short of legalizing gay marriage - as was done in Spain and other European countries. Rather, it would entitle unmarried couples who live together to rights such as hospital visiting rights and inheritance rights.
Critics, including the demonstration organizers, say the bill would dismantle what they consider to be the centerpiece of society: the traditional family based on marriage between man and woman. Supporters argue the bill doesn't create an alternative family model, and say recognizing the basic rights of people who live outside marriage would make Italy a more civilized country.
As the bill awaits to be taken up by parliament, its fate is anything but certain. Prodi has left lawmakers in his divided coalition free to vote according to conscience.
The bill has irked the Vatican, which under Benedict has been conducting a fierce campaign to protect traditional families.
"Family deserves a priority attention, as it is showing signs of collapse under pressure from lobbies that are capable of negatively affecting the legislative processes," the pope said recently. "Only on the rock of marital love between a man and a woman, solid and faithful, can we build a community worthy of a human being."
Benedict is currently on a visit to Brazil. His message has been taken to heart by the Italian bishops' conference, which in a country where over 90 percent of people are at least nominally Roman Catholic still holds a degree of influence. The bishops expressed their support for Saturday's rally in a statement at the end of their most recent assembly in March.
Tensions were heightened last month when graffiti threatening the head of the Italian bishops, Genoa Archbishop Angelo Bagnasco, were scrawled on buildings in the northern city and a bullet was sent to his office. Bagnasco has spoken out strongly against the proposed legislation.
The Italian Catholic Church has been active on the domestic political front in recent years, weighing in on issues ranging from the right to die to assisted procreation and bioethics.
Late last year, church officials denied a religious funeral for a paralyzed man who had a doctor disconnect his respirator. The church decision angered relatives and right-to-die activists.
In April 2005, the Vatican spearheaded a successful campaign asking Italians to boycott a referendum on easing assisted fertility restrictions. That battle was reminiscent of church campaigns urging Italians to vote against laws permitting divorce and abortion - but those efforts failed in referendums in 1974 and 1981, respectively.
Demonstration organizers say the rally should not be colored with political overtones or be seen as an anti-government protest.
But the event has already proven embarrassing for Prodi's coalition, with at least one minister saying he would take part. Separately, other center-left leaders said they would attend a counter-demonstration planned also Saturday in Rome's Piazza Navona, expected to be much smaller.