A senior Catholic figure in Scotland is using the hotly contested Glasgow East by-election to push a controversial anti-government message in the apparent hope that voters will punish it for defying the church.
Bishop Joseph Devine, whose diocese covers the contested constituency, has launched a strong attack on Prime Minsiter Gordon Brown's government over the bill, accusing it of "violating moral law" and "losing ethical credibility".
Cardinal Keith O'Brien, whose earlier comments on "Frankenstein research" were widely condemned as emotive and inaccurate, has also joined the fray.
Labour is defending a previously "safe seat" from the Scottish Nationalists (SNP), whose candidate is a Baptist with strong views on social justice.
He also favours a reduction in the legal time limit on abortion (currently 24 weeks), unlike the other main candidates, including Labour, the Liberal Democrat and the Conservative.
Catholic leaders in Scotland are angry at Labour MPs for supporting the Human Fertilisation and Embryology (HFE) Bill, which will pave the way for research involving admixed embryos, and at the party's failure to back a lower time limit for abortions.
Last week, the government postponed a parliamentary debate on the HFE bill, and its critics say this was influenced by fears it could dent its vote in Glasgow East - which has a strong Catholic base.
The Human Fertilisation and Embryology Bill will now not complete its final stages until the autumn. It has been strongly backed by the former Anglican Bishop of Oxford, Lord Harries, among others, indicating a division of opinion among Christians as well as among those of other faith or no religious convictions.
But Bishop Devine has written to Labour MPs, claiming that although the government had won a Commons vote on the bill in May 2008, it had "in the process, lost its ethical credibility".
Speaking during the first televised debate between the four main candidates for the by-election, Labour candidate Margaret Curran was asked about her stance on the HFE bill. She said: "I have followed the debate and, broadly speaking, I would vote with the government."
On abortion, she declared: "As things stand at the moment, I am not persuaded that there is any need to change the current law."
Also talking on the Politics Show Scotland debate, Mr Mason said: "I am coming from a faith community background and I am extremely unhappy about any experiments on babies or research, or anything like that."
Asked whether he wanted to reduce the time limit for abortions, he replied: "Yes."
The by-election has been seen, up until now, as a straight fight on politics between Labour and the SNP. But Glasgow East has one of the highest Catholic populations in the country – more than a third of voters, according to the last census.
On a low poll turnout, that might prove to be significant says some observers.
Bishop Devine's strictures may be heeded by some voters. However, past polling evidence suggests that ordinary Catholic voters are not necessarily persuaded by what critics see as "hectoring" from the hierarchy.
Current polls indicate that Labour is set for victory, albeit with a reduced majority.