Welsh Labour leadership candidate Mark Drakeford has dismissed the environmental benefits of nuclear power, referring to the disasters of Chernobyl and Fukushima.
He said people at both places would not want to be told this was how “your environment will be safeguarded”.
The comment at a 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 rivals over his “sceptical” stance on nuclear power.
“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.”
Vaughan Gething supporter and Labour Caerphilly AM Hefin David 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.”
Mr Gething and Eluned Morgan have previously said Mr Drakeford’s views could hit prospects for the proposed Wylfa Newydd nuclear power station.
Mr Drakeford said at the time that the local impact of the planned plant on Anglesey should be borne by the developers, but that did not mean that the plant cannot be built.
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.
Outgoing First Minister Carwyn Jones has said Wylfa Newydd has the potential “to transform the Welsh economy”.
‘Biased and partisan’
Mark 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.”