The Catholic Church in Scotland has joined the row over gay rights laws.
Archbishop Mario Conti has written to the first minister
The Archbishop of Glasgow wrote to the prime minister and Scotland's first minister, saying new measures would be "a betrayal" of previous commitments.
Archbishop Mario Conti's letter comes after the head of the church in England warned the laws could prompt the closure of Catholic adoption agencies.
The church wants to continue its policy of referring gay couples to other adoption agencies.
But this could fall foul of the Equality Act, due to come into effect in England, Wales and Scotland in April.
There are two Catholic adoption agencies in Scotland.
The Scottish Parliament passed legislation in December allowing unmarried and gay couples to adopt, despite staunch opposition from the church.
It makes no exemptions for Catholic adoption agencies but church leaders say ministers assured them their position would be protected.
In his letter, Archbishop Conti said: "The Catholic Church in Scotland also provides adoption and fostering services and the proposed regulations put in jeopardy the ability of these agencies to retain the discretion they have always exercised in favour of the children entrusted to them, which discretion is informed by the moral and social teaching of the Catholic Church."
He added: "Implementation of the proposed regulations would be regarded as a betrayal of this commitment which was accepted in good faith by the Catholic community in Scotland."
The first minister's spokesman said he would not comment on the letter at this stage.