An archbishop has called on MSPs to vote against giving homosexual partners the same legal rights as married couples.
Glasgow's Archbishop Mario Conti said the plans, outlined in a private members' bill set to be tabled by Green MSP Patrick Harvie, were "subversive".
He also called on Catholic politicians to follow their consciences rather than the party whips when the time came to vote on the matter.
The archbishop spoke out after the Vatican re-stated its opposition to same-sex unions.
Mr Harvie's Civil Partnerships (Scotland) Bill would provide unmarried couples in "committed" relationships with equality in areas like inheritance, pensions and bereavement.
But The Most Rev Conti said MSPs should reject the proposed legislation.
He said: "The only privileged legal union in society is the family.
"Attempts to give equivalent rights and legal recognition to other unions would be subversive of the right order - it is not for the law to reconstruct humanity.
German couples have been granted inheritance and tenants' rights
"It is important that all citizens are able to protect their legitimate interests.
"Many existing legal mechanisms allow this without compromising the primacy of marriage as the most secure and stable building block of civil society."
Similar plans to give legal recognition to non-married couples have been unveiled at Westminster.
But Catholic Church spokesman John Deighan said he hoped MSPs would support the stance of the church by not backing the bill.
Speaking on the BBC's Good Morning Scotland programme, he said: "It is not homophobia and we have no gripe against homosexuals per se but we believe that the homosexual relationship is subversive."
Mr Harvie, a Glasgow list MSP, has offered to meet the Catholic church to discuss his bill.
He said: "An MSP, or any other elected politician, has a duty to serve all their constituents, whatever their sexuality and whatever their religion.
"As an MSP, I wouldn't tolerate this level of discrimination in law against Catholics or any other religious minority or majority and I don't think that Catholic MSPs should tolerate this kind of discrimination.
"We're not proposing to reconstruct humanity, we simply want the state to support all families on their own terms."