Largest evangelical churches against gay marriage
Scotland's largest evangelical churches are calling on the first minister not to change the law defining marriage.
A letter of opposition to same-sex marriage will be delivered to Alex Salmond at St Andrew's House in Edinburgh.
It follows a Scottish government consultation on the issue.
More than 50,000 responses were submitted before the consultation closed last Friday. A report on the matter will be published in the spring.
Representatives from more than 70 of Scotland's largest evangelical churches signed the letter to Mr Salmond.
It states: "In supporting marriage, we are not removing rights from anyone. Redefining marriage is not an issue of equality or fairness, as argued by those calling for this change. Equality does not mean sameness but recognises diversity.
"In the Scottish government's consultation document it is abundantly clear that homosexual couples already have the rights of marriage available through civil partnerships.
"Despite the sincere promises to protect those who disagree with redefining marriage, we have well-founded misgivings about the religious liberty implications. However, our chief concern is that Scottish society will be the poorer if the definition of marriage is rewritten. Marriage is foundational and so much else rests upon it.
"You cannot radically alter the definition of marriage without it having knock-on effects on so much else in our society."
The letter will be handed over by three signatories, Reverend Alex Macdonald, Reverend Jeremy Middleton and Reverend David McCarthy, who will then take part in a rally.
Equal Marriage campaigners have submitted around 18,000 responses to the government's consultation.
Gay equality charity Stonewall Scotland is sending postcards to MSPs urging them to support same-sex marriage.
Scotland's deputy first minister, Nicola Sturgeon, said all views would be listened to, but added that ministers "tended towards the initial view" that same-sex marriage should be introduced.