MPs in Poland have begun debating controversial plans to liberalise IVF treatment amid staunch opposition from the Roman Catholic Church.
One archbishop has said Catholic MPs face excommunication if they opt to regulate in-vitro fertilisation in the country.
The government says such statements amount to "blackmail".
The options range from a total ban on IVF, punishable by prison, to state authorisation and reimbursement.
IVF is the process by which egg cells are fertilised outside the body before being implanted in the woman.
Despite being unregulated, it is widely used in Poland to help couples who are having difficulty conceiving.
On Monday, Catholic bishops, who play an influential role in Polish society, sent a letter to political leaders calling IVF "the little sister of eugenics".
Eugenics is a practice aimed at changing the genetic characteristics of human populations, and was notably used by the Nazis.
The bishops wrote that "IVF requires the selection of embryos, which means killing them".
One of the signatories to the letter, Archbishop Henryk Hoser, said in an interview MPs who supported IVF would "find themselves automatically outside the community of the Church".
"A child must be conceived in a natural way," he said.
A spokesman for the centre-right government, Pawel Gras, said: "The threats and attempts to blackmail are amazing."
President Bronislaw Komorowski, himself a Catholic and father-of-five, has called for a reasonable compromise that respects both Christian sensibilities and the needs of "many, often desperate couples, seeking a way to have a child".
Prime Minister Donald Tusk said politicians were responsible to citizens, not the Church hierarchy.
He is supporting a draft tabled by his Civic Platform party which authorises the freezing of additional embryos for possible future use. An alternative draft does not allow for this freezing process.
Poland's main conservative opposition Law and Justice Party wants IVF banned, while some ultra-conservative groups are pushing for it to be criminalised.
The BBC's Adam Easton in Warsaw says according to surveys, most Polish people, despite being Catholic, want IVF to be available for married couples.
He says it seems likely the politicians will ignore the bishops' advice to ban the practice.