Welsh Labour leadership candidate Mark Drakeford has been criticised for dismissing the environmental benefits of nuclear power by referring to the disasters of Chernobyl and Fukushima.
Supporters of rival Vaughan Gething called Mr Drakeford's comments reckless and "outdated".
The discussion at a leadership hustings was leaked to BBC Wales.
Mr Drakeford called the leak "highly biased and partisan", saying no-one should rely on it to judge his views.
He has faced criticism from rival contenders Vaughan Gething and Eluned Morgan over his "sceptical" stance on nuclear power, with both claiming it could damage the prospects of the proposed Wylfa Newydd power plant on Anglesey.
Mr Drakeford argues the local impact of the planned plant on Anglesey should be borne by the developers, but says that does not mean that the plant cannot be built.
"I said to Eluned in an earlier debate that her belief that nuclear power is somehow an advantage to the environment: tell that to the people in Chernobyl, tell that to people in Fukushima," Mr Drakeford said at the hustings in Newport on Thursday.
Amid groans of disapproval from the audience, he said: "You may not like it, but you wouldn't like it if you were living there either, and being told this was the way that your environment will be safeguarded for the future."
In response, Mr Gething told the hustings: "To talk about Wylfa in the same breath, again, as Chernobyl, Fukushima and Three Mile Island I think is deeply damaging to the prospect of any further investment in that industry in the future.
"We should not develop such an openly hostile view to those jobs," Mr Gething added.
The Wylfa Newydd scheme is projected to employ around 9,000 people.
Mr Drakeford later told the hustings he had the backing of Ynys Mon's Labour MP Albert Owen.
"If that doesn't tell you that the idea that my views are somehow hostile to Wylfa is not true, then I don't know what else I can do to persuade you", he said.
Labour Caerphilly AM Hefin David - who backs Vaughan Gething for leader - said: "In these difficult times we should think carefully about the words we use.
"There is a certain recklessness in this comparison that I'm sure wasn't intended by Mark Drakeford."
Mike Payne, political officer for Wales of the GMB union which is supporting Mr Gething, said: "It's always disappointing to hear outdated views preventing a serious discussion about securing our energy future and workers' jobs in Wales."
The winner of the Welsh Labour contest would take the helm of the Welsh Government as first minister - but he or she would not have powers over large power stations including Wylfa.
In contrast, outgoing first minister Carwyn Jones has said Wylfa Newydd has the potential "to transform the Welsh economy".
'Importance of Wylfa'
Mr Drakeford told BBC Wales: "No-one should rely on a highly biased and partisan leak from a private meeting to characterise the views of any candidate in this election.
"I have said repeatedly that I recognise the importance of the Wylfa Newydd development on the island of Anglesey.
"The role of government is to ensure that, as this goes ahead, the long-term interests of Anglesey residents are protected and that the developer meets all its obligations.
"If I were to be first minister then I would ensure that the Welsh Government works with all those local interests to secure exactly that outcome."