Scottish Catholics are to be warned by their bishops that taking the morning-after pill, authorised for sale to over-16- year-olds by the government earlier this year, is the equivalent of a "chemically induced abortion".

In a pastoral letter, signed by all eight bishops, to be read out at masses in coming weeks, congregations will be told: "The church cannot remain silent on this issue, given the serious nature of what is being proposed."

It will exert moral pressure on Catholic doctors and pharmacists as well as parents and teenagers to refuse to sanction the use of the pill, calling on them "to reflect on what is being proposed and to exercise their conscientious right of objection."

It is estimated that more than 700,000 of Scotland's 5m inhabitants are at least nominally Catholic.

The statement adds: "By offering over-the-counter potentially abortifacient drugs to 16-year-olds, parental rights are being undermined and family bonds weakened.

"If our teenagers feel they are so unimportant that we can leave this aspect of their healthcare to a 10 minute chat in a busy pharmacy, with a pharmacist who cannot carry out any physical examination, or consult medical records, we are sending out a regrettable and dangerous message to a highly vulnerable group."

The letter is being sent out in the name of Cardinal Thomas Winning, leader of the church in Scotland and president of its bishops' conference, who has led a long campaign against abortion rights, even funding young women who opt not to terminate their pregnancies. He has condemned the government for not banning abortion.

The pastoral letter claims that attempts to cut teenage pregnancy rates may inadvertently push up rates of teenage sexual activity, sexually transmitted diseases and abortions.