Research using hybrid human-animal embryos for experiments is "monstrous" and should be banned, the leader of the Roman Catholic Church in Scotland said on Friday.
Cardinal Keith O'Brien said a proposed new law - the Human Fertilisation and Embryology Bill - should outlaw the practice.
The House of Lords rejected attempts earlier this year to include a ban on hybrid research in the draft legislation.
"This Bill represents a monstrous attack on human rights, human dignity and human life," O'Brien will say in his Easter Sunday sermon, according to extracts published in Friday's Daily Record newspaper. "In some other European countries, one could be jailed for doing what we intend to make legal."
In an interview with BBC radio on Friday, he added: "This is Frankenstein science and it must be stopped."
Scientists said the cardinal did not understand the issue properly and accused him of "scaremongering".
Supporters of hybrid research say it will give scientists the large number of embryos they need to make stem cells to help find cures for a range of diseases.
Researchers create inter-species hybrids by injecting human DNA into a hollowed-out animal egg cell. The resulting embryo is 99.9 percent human and 0.1 percent animal.
Britain is one of the leading states for stem cell research, attracting scientists from around the world with a permissive environment that allows embryo studies within strict guidelines.
Scientists in China, the United States and Canada have carried out similar work, the same technique used to create Dolly the sheep, the world's first cloned mammal.
Dr Stephen Minger, director of the Stem Cell Biology Laboratory, King's College London, said the cardinal "didn't understand the basic facts".
"The church should carefully review the science they are commenting on, and ensure that their official comments are accurate, before seriously misinforming their congregations," he said in a statement.
Dr Lyle Armstrong, of the Institute of Human Genetics at the University of Newcastle upon Tyne, northeast England, said: "The aim of our experiments is to discover ways to make stem cells for anyone that will be invaluable in treating human diseases, not to give birth to some abnormal chimaera."
The BBC reported on Friday that at least one member of the cabinet may resign over the proposed law. It did not name the politician.
A spokeswoman at the prime minister's office said there would be no response to the cardinal or the BBC report.
The Human Fertilisation and Embryology Authority, which regulates the research, gave permission to two groups of UK-based scientists to use hybrids in January.
The draft law is making its way through parliament and is due to return to the House of Commons in the coming weeks.
