One Catholic member of the ruling Labor Party in the New South Wales state parliament said he would rather go to hell than take orders on how to vote from Sydney Catholic Archbishop George Pell.
"Maybe I'll go to hell, but if I go to hell I'm going to do so by saving a lot of lives, because that's what this bill is about," Tony Stewart said in a radio interview.
"We don't need a religious leader telling members of parliament what should be done." Lawmakers are being allowed a conscience vote on a bill to bring the country's most populous state into line with the federal government, which overturned a ban on therapeutic cloning last year.
The new law would allow excess human embryos from in-vitro fertilisation treatment to be used to create stem cells for research into fighting debilitating diseases such as Alzheimer's, Parkinson's and cystic fibrosis.
"Cloning is not quite the same as abortion and the legislation for such a thing as cloning is different from actually performing cloning," Cardinal Pell told reporters.
"But it is a serious moral matter and Catholic politicians who vote for this legislation must realise that their voting has consequences for their place in the life of the church." Pell said he was not threatening to excommunicate Catholic lawmakers who voted in favour of the bill, but indicated he was considering refusing them holy communion.
Both state Premier Morris Iemma and his deputy John Watkins, who are Catholics, have said they would defy Pell's warnings and vote for the bill.
Another Catholic MP, Adrian Piccoli, said of the threat of being refused communion: "I would like to see them try and stop me." Pell said the bill would allow for unethical research that could see the creation of human and animal hybrids.
"These possibilities are quite grotesque," he said.
"I'd be very surprised if they had approval throughout the population." The Anglican church is also asking MPs to vote against the bill.
But the Minister for Science and Medical Research, Verity Firth, denied scientists would be given carte blanche for research and said she was confident the bill would pass both houses of parliament.