The campaign, supported by among others the Catholic Bishops' Conference of Scotland and The Christian Institute, said legal opinion it had commissioned from leading QC Aidan O'Neill showed that equalising marriage would have a "draconian impact" on Scotland.
This would include:
l Priests and ministers being sued for refusing to allow gay marriages in their churches;
l workers facing the sack for opposing same-sex unions;
l schoolchildren being "forced to attend gay history lessons"; and
l couples being rejected as foster parents if they opposed the new equality legislation.
A campaign spokesman said: "This judgment lays bare Scottish Government promises of exemptions and protections for churches as completely worthless.
"This detailed legal analysis shows same-sex marriage is not about allowing same-sex couples to walk up the aisle as politicians and campaigners have wrongly claimed, it is about redefining society."
The campaign said Holyrood's proposed exemption allowing priests and ministers to refuse to hold a gay marriage would be worthless because the new law would become a "stepping stone for the gay rights lobby, using European human rights legislation, to eventually force the Government to capitulate and remove the clauses preventing the performance of the same-sex marriages by certain institutions or individuals".
The UK Government, which is also proposing an exemption for churches and other religious institutions, continued to insist yesterday that, according to its legal advice, "no Church of England minister should face a legal challenge" if they refused to solemnise a gay marriage.
However, Justice Minister Crispin Blunt conceded the aim of exempting religious groups from offering gay marriage might be "problematic legally".
Already, Cardinal Keith O'Brien, head of Catholics in Scotland, has lambasted the UK and Scottish governments for considering introducing gay civil marriage, saying it was a "grotesque subversion of a universally accepted human right".
Yesterday, the Roman Catholic Church in England and Wales joined the Church of England in attacking the proposed equalisation of marriage.
Catholic bishops south of the Border described marriage as a "unique institution" whose distinguishing characteristics centred on the "biological complementarity" of men and women and the possibility of children.
A 500,000-strong petition opposing same-sex marriage was handed into Downing Street by the Coalition for Marriage.
Earlier, the Church of England warned legalising gay marriage could lead to it being forced out of its traditional role in wedding services and cause the biggest rupture with the state for 500 years. It even hinted the move could unravel its role as the established church.
Gay rights campaigners accused it of overreacting and of performing a "master-class in melodramatic scaremongering".
The controversial subject is set to become a political headache for Alex Salmond before it becomes one for David Cameron.
The Scottish Government's consultation, which received more than 50,000 responses, ended in December and the results are due to be published within a fortnight.
The UK Government's – which is thought to have attracted the biggest reaction ever to a public consultation with more than 100,000 responses – ends today with the results due before the end of the year.