Mexico's Catholic Church leaders have criticised a government decision to allow the so-called morning-after pill.
The Archbishop of Mexico City is a leading opponent of the pill
Use of the emergency contraceptive was approved last week in an amendment to family-planning guidelines.
But some Church figures have said that the Church cannot remain silent on the issue, saying use of the contraceptive pill is comparable to murder.
Health Department statistics show that around 40% of Mexico's 2.1million pregnancies a year are unplanned.
One of the leading opponents of the measure is the Archbishop of Mexico City, Cardinal Norberto Rivera Carrera.
"Although they may be called contraceptives, when they produce an abortion, it is called murder. It is forbidden to kill the innocent," he said.
Other Church leaders have gone as far as to suggest women who take the pill will face effective excommunication from the Church.
Among them is Jorge Palencia, a priest in charge of health in the First Archdiocese of Mexico.
"The Church cannot stay silent faced with genocide of the magnitude which is on its way," the Spanish news agency Efe quotes him as saying.
He said that those who took the pill would not be excommunicated by official Church action, but spiritually through their own actions.
But the government has defended its sanctioning of the morning-after pill, which went through along with approval of the female condom.
"In Mexico, it wasn't possible earlier to include (the pill) in official family planning laws because of the opposition of conservative groups who absurdly qualified it as abortive," said Gregorio Perez, the Health Department's ex-Reproductive Health director.
The morning-after pill is a higher dose of regular hormonal contraception.
Taken within 72 hours of intercourse, the pill prevents a fertilised egg from attaching to the lining of the womb.
It has no effect if a woman is already pregnant, which is why it has not been as controversial as the abortion pill RU-486.
But it is opposed by critics who object to any interference with a fertilised egg.