The Christian Institute has called it a "very sad development" after most presbyteries in the Church of Scotland came out in support of same-sex weddings in its church buildings.
A report to the 2022 General Assembly shows that 29 presbyteries gave their backing to legislation which, if passed, will allow ministers to conduct marriage ceremonies for gay couples.
Twelve presbyteries voted against the draft legislation.
The report to the forthcoming General Assembly says that no minister will be forced to wed a gay couple or be involved in the arrangements.
The legislation is to be debated at the General Assembly, taking place online and in Edinburgh from 21 to 26 May.
Under the proposals, ministers will be able to apply to the Principal Clerk's office to become a celebrant of same-sex weddings. An application would then be made to the Registrar General for Scotland on their behalf.
The legislation requires that in deciding whether to conduct a same-sex marriage ceremony, approved celebrants take account of the "peace and unity and pastoral needs of the congregation and any parish or other grouping of which it is a part".
If the legislation is passed, liturgy will be drawn up specifically for use in same-sex marriage ceremonies.
Responding to the news, The Christian Institute's Scotland Officer Nigel Kenny commented: "This is a very sad development in the life of the National Kirk, which has in its constitution a commitment to the Bible as the supreme authority in all matters of faith and practice.
"The Bible is crystal clear that true, God-honouring marriage is only between one man and one woman. Jesus' own teaching on this in Matthew 19 could not be clearer. But it seems that the majority of presbyteries are more interested in taking their cue from culture rather than Christ."