The Vatican is issuing new instructions to bishops and Catholic politicians in an effort to halt the growing legal acceptance of gay marriages.
The instructions are in a document prepared by the Church's guardian of orthodoxy, the Congregation for the Doctrine of the Faith.
It is titled, Considerations Regarding Proposals to Give Legal Recognition to Unions Between Homosexual Persons.
Pope John Paul and top Vatican officials have been speaking out for months against legislative proposals to legalise same-sex marriages in Europe, North America and elsewhere.
In January, the Pontiff approved guidelines for Catholic politicians that said church opposition to abortion, euthanasia and same-sex marriage was not up for negotiations.
It said laws safeguarding marriage between man and woman must be promoted and that "in no way can other forms of cohabitation be placed on same level as marriage, nor can they receive legal recognition as such."
But legal acceptance is growing.
Two Canadian provinces - Ontario and British Columbia - have legalised homosexual marriage under recent court rulings, a move that has attracted gays from across the border in the United States.
Earlier this month, a top German cardinal condemned Germany's same-sex marriage law after it was upheld by the country's supreme court, calling it a blow to the family.
The Vatican is particularly worried about the waning influence of the church in Europe. Drafters of a proposed constitution for the European Union ignored Vatican requests to include explicit mention of Europe's Christian roots.