Pope Benedict XVI told Catholic politicians on Tuesday that they must not vote for laws which go against Church teaching on issues such as gay marriage or abortion.
In a document summing up discussions at a meeting of bishops held in the Vatican in 2005, the pope said that Catholic legislators must be "aware of their social responsibility" and so cannot vote for laws that go against "human nature".
They must strenuously defend the Church's "non-negotiable values", which are "respect for human life" and "family based on marriage between man and woman", he added.
Benedict's statement was seen as a clear reference to moves in several Catholic countries to introduce gay marriages, or at least to give legal recognition to gay couples.
Spain has already introduced gay marriage and Italy, home to the Vatican, is currently debating whether to give certain rights to unmarried couples, including gay ones.
The pope's reference to "defence of human life" appeared to be a swipe at politicians in countries such as the United States, where some Catholic lawmakers have argued they must support measures allowing abortion because their voters want them.
Politicians must give "public testimony to their faith", the pontiff said.
On other points, Benedict called for Sunday to remain a day of rest and for trainee priests to prepare to celebrate mas in Latin and to use ancient Gregorian chants in church.
Speaking to bishops, he reminded them of their duty to "constantly recall" the Church's non-negotiable values, saying "this is part of their responsibility towards the flock entrusted to them".
Touching on a point which has created tensions in the US Catholic Church, he stated unambiguously that bishops should not allow remarried divorcees to receive communion.
REACTION IN ITALY.
The document, or Apostolic Exhortation, drew criticism in Italy from leftwingers who said it amounted to interference in national politics.
"The pope's claim to be the interpreter and repository of absolute truth, of the only plausible morality...is frightening," said Franco Grillini, a gay MP belonging to the Democratic Left, the largest party in the government.
But there was also applause from Catholic lawmakers, such as Maurizio Lupi of the centre-right opposition party Forza Italia.
"We thank the pope for his judgment which he gives us as free and responsible politicians. Now no one can hide," he said.
In coming weeks the Italian bishops' conference is expected to publish a document advising Catholics in parliament on how to act when a bill on rights for cohabiting couples comes up for approval.
