The leader of Roman Catholics in England and Wales has urged the faithful to write to their MPs to oppose the Government's plans for gay marriage.
The Most Rev Vincent Nichols, Archbishop of Westminster, called on Roman Catholics to express their views "clearly, calmly and forcefully".
He said one of his concerns about the plans was how children would be taught about the "true nature of marriage" in schools if the law is changed to allow same-sex marriage.
"Of course there are many different circumstances to family life. Events reshape the family lives of many people," he wrote in a pastoral letter read out in parishes in the Diocese of Westminster over the weekend.
We are right to express our admiration for those who work so hard to maintain family stability in difficulty and isolation.
Support and loving care for them can make all the difference.
But none of this takes away the importance of having a clear vision of marriage and family, based on human nature itself.
I urge everyone who cares about upholding the meaning of marriage in civil law to make their views known to their Members of Parliament, clearly, calmly and forcefully.