The church cannot remain silent on this issue, given the serious nature of what is being proposed.

Catholic bishops

The bishops contend that families, schools, churches and government all have a role in making unwanted pregnancy "a problem of the past," but suggest the government's new approach is "sidelining" parents and undermining family relationships.

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

The bishops state: "The church cannot remain silent on this issue, given the serious nature of what is being proposed."

They say their opposition to the morning after pill is as much based on their opposition to abortion as it is to the church's well-known opposition to contraception.

Chemically-induced abortion

The letter says the pill may prevent ovulation and thus fertilisation, but it goes on: "Depending on when it is administered it can also prevent tiny a human being, or embryo, which has come into existence at the moment of conception, from implanting in the mother's womb.

"This leads to the death of the embryo. In such cases we are dealing with chemically-induced abortion."

They add: "In stating these simple facts we are not seeking to impose our views on others. Instead, we aim to propose for public consideration the truth about these drugs.

"In ethical terms, the church considers the prescription, supply and consumption of potentially abortifacient drugs to be very wrong. We call on doctors, pharmacists, parents and teenagers to reflect on what is being proposed and to exercise their conscientious right of objection."