A letter criticising the Scottish Government for supporting plans to legalise gay marriage has been read out in all of the country's Catholic parishes.
The Roman Catholic Church declared August 26 as National Marriage Sunday and is calling on politicians to "sustain rather than subvert marriage".
The letter, which was expected to be read in all of Scotland's 500 Catholic parishes, will urge followers to continue to act against efforts to "redefine" marriage.
The Scottish Government has said it is right to introduce same-sex marriages, but has stressed no clergy would be forced to carry them out.
Cardinal Keith O'Brien, the leader of the Church in Scotland, last week broke off discussions on the issue with First Minister Alex Salmond.
In a strongly worded message, the letter highlights the church's "deep disappointment that the Scottish Government has decided to redefine marriage and legislate for same sex marriage."
It also announced the launch of a National Commission for Marriage and the Family to co-ordinate a campaign against gay marriage.