JACK McConnell will today face fresh pressure to allow the building of new nuclear power stations in Scotland.
Unions are set to endorse the idea of a "balanced" energy policy - including new nuclear stations and prolonging the life of existing ones.
The move, at the Scottish Trades Union Congress this week, increases the pressure on Mr McConnell to move away from his position - agreed with his anti-nuclear Liberal Democrat coalition partners - that he will not decide on the building of new nuclear stations until the issue of the safe disposal of waste is resolved.
The driving force is the Amicus union which represents many of the workers in the nuclear industry in Scotland.
A motion to the STUC calling for a mix of energy suppliers in Scotland, which has the support of other unions including the National Union of Mineworkers, is likely to be passed despite opposition from some unions.
John Quigley, the Scottish secretary of Amicus, has said that the union is sceptical about relying on renewable energy - wind and wave power - to fill the gap when nuclear stations have to be decommissioned.
A source in the STUC said last night: "The final details of the motion are being agreed ahead of the debate but it is clear that we are likely to back a mixed energy policy. No-one believes that we can rely completely on renewable energy sources."
The issue of nuclear power could be a "coalition-breaker" in the next Executive if Labour and the Lib Dems try to form another devolved government.
Under pressure from his party, the unions and Downing Street, where the Prime Minister is said to favour a new generation of nuclear stations, Mr McConnell is thought to be moving towards giving his endorsement to a mixed energy policy.
However, Nicol Stephen, the deputy First Minister and leader of the Lib Dems in Scotland, has set his face against any new nuclear power stations.
Scottish ministers have the devolved power, under UK legislation, to give the go-ahead for any new stations north of the Border and they also control the planning process.
The motion, put forward by Amicus but including the views of other unions, welcomes the UK government's decision to have an energy review.
It says that "the importance of a safe, secure and diverse means of electricity production cannot be over-emphasised", because of the key role it will play in the future energy costs to the UK economy.
The motion further calls on the government "to adopt a balanced energy policy to meet the energy needs of the nation".
It adds: "This review must include the promotion of clean coal technology and consideration of new nuclear build, as well as oil and gas, and renewables, in order to avert the nation's energy needs being held hostage to politically unstable states."
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