A campaign group will gather outside the Scottish Parliament to rally against proposed changes to the law which would legalise same-sex marriage.
Cardinal Keith O'Brien, the leader of the Catholic Church in Scotland, former SNP leader Gordon Wilson and Ann Allen of the Church of Scotland will be the keynote speakers at the Scotland For Marriage event.
The group supports the current legal definition of marriage and is resistant to plans to redefine it.
The Scottish Government launched a consultation in September asking if marriage in Scotland should be allowed for gay people through a civil or religious ceremony.
Currently, same-sex couples can enter a civil partnership which carries full legal rights but the ceremony cannot be conducted in a church or other religious premises.
A recent Scottish Social Attitudes survey found that more than 60% of people believe same-sex couples should have the right to marry, compared with 19% who disagree.
Ministers and officials have been meeting with key groups to discuss the proposals, which would ensure religious organisations do not have to register same-sex marriages against their will.
The rally is the latest step in opposition to the proposals, and will include the delivery of around 20,000 postcards to the Parliament signed by those who do not want same-sex marriage to be legalised.
The three keynote speakers will also sign a petition, calling for a referendum on the issue and expressing concerns about the wider implications of redefining marriage.
Meanwhile, adverts will appear in newspapers and a poster van advertising the launch of the campaign group will drive around the streets of Edinburgh.