Over 300 jobs at ESB and Bord na Mona are at risk in the midlands.
It's after planning permission to redevelop a power station was refused.
The proposals for the facility in Shannonbridge, Co Offaly would have seen it fuelled with biomass as well as peat.
But environmental groups opposed the plans- saying it wouldn't lead to a reduction in carbon emissions.
And it's environmental concerns which is one of the main reasons An Bord Pleanala has turned down planning permission.
There's now uncertainty for the hundreds of workers at the site.
Environment Minister Richard Bruton hopes anyone who loses their job can switch to more sustainable industries.
Speaking on RTÉ radio’sMr Bruton said that both the ESB and Bord na Mona will have to assess the impact of the decision which trade unions are warning could mean hundreds of job losses.
The decision by An Bord Pleanála will have to be studied in depth so they can evaluate the best way forward.
The Government wants to ensure that Bord na Mona’s plan remain a priority, he said. “Bord na Mona has plans to develop alternative power sources such as wind, waste management and recycling, horticulture and aquaculture.
“This was a plan for the future. We will have to see why this decision was made.”
Mr Bruton said it had been clear for some time that there had to be a move away from peat which made the decision disappointing.
However, Siptu says workers are being thrown off a cliff.
ESB Group of Unions secretary, Willie Noone, said: “The news today, that An Bord Pleanála has refused Shannonbridge Power Station in county Offaly a licence to develop a biomass fuel firing system threatens hundreds of jobs in the midlands region.
“It is now highly likely, that due to increasing costs, the ESB may deem the continued operation of Shannonbridge Power Station unviable as early as January 2020, although it does have a licence to continue burning peat until the end of next year," he added
This means that over 300 direct jobs are at risk with hundreds more that indirectly rely on the operation of the power station are also under threat
Last week, the temporary closure of a power-plant at Lanesboro, Co Longford, which Bord na Móna supplies was announced.
This led to a protest yesterday
“With the future of Lough Ree Power Station in county Longford also on a knife edge the Bord na Móna Group of Unions is calling on Minister for Communications, Climate Action and Environment, Richard Bruton, to take direct responsibility in finding a solution to a crisis which threatens to economically devastate the midlands."
Fianna Fáil TD for Offaly, Barry Cowen, has said the decision made by an Bord Pleanála to refuse planning permission for the redevelopment of an ESB power station to co-fuel the Shannonbride power station with biomass must be appealed.
“We have known for a long time that Bord na Móna will be diversifying over the coming years, but there must be time to transition," he said.
"You can’t shut up shop on an entire industry which has provided employment for successive generations without first putting in place tangible alternatives and safeguarding the local economy," Mr Cowen added.