Delegates at Labour's Scottish conference in Aviemore have endorsed a resolution backing the replacement or renewal of nuclear power stations.
Hunterston B is scheduled to close in 2011
The Amicus engineering union, who had called for the move, said it should be part of a balanced energy policy.
Labour's coalition deal with the Lib Dems in Scotland states new nuclear power stations will not be built before the issue of waste is dealt with.
The Nationalists and Greens condemned Labour's endorsement of more nuclear.
Scottish National Party energy spokesman Richard Lochhead said it was a "crazy and utterly irresponsible decision".
He said: "Scottish public opinion is opposed to nuclear because it is dangerous, dirty and expensive and Labour's anti-Scottish policy will undermine efforts to turn Scotland into Europe's clean energy capital."
The Scottish Greens reacted with dismay and described support for nuclear power without resolving the waste problem as "immature" and "irresponsible".
Green MSP Chris Ballance said: "This shows that at heart Labour is wedded to the nuclear dinosaur rather than the renewable technologies of the future.
"There is no need to go nuclear, neither is it wanted by Scotland's people.
"We have renewable energy sources in abundance, and we have to get serious about reducing energy demand."
Moving the resolution at the conference, Hugh Scullion of Amicus said: "We support a balanced energy policy that promotes the use of all available energy in the most productive manner possible.
"This should include conventional fossil fuels, coal and oil, gas, renewables and nuclear."
Deputy enterprise minister Allan Wilson urged everyone to keep an open mind on the issue.
He also restated the executive's position on nuclear power, saying: "We will not sanction the development of any new nuclear power stations while the issue of nuclear waste remains unresolved."
Scotland's two existing nuclear power stations, at Hunterston on the Clyde coast and Torness in East Lothian, provide 40% of Scotland's electricity.
Hunterston B is due to close down in 2011 but a 10 year extension is being discussed. Torness is also due to close within the next 20 years.