Christmas dinner could be on hold if strikes at power plants at Hunterston go ahead, plunging households around the country into darkness.
GMB has threatened industrial action at Hunterston B and Torness during the festive period, which could leave Scotland without a third of its electricity supply, it has been claimed.
Union members say they are 'locked in a dispute' with EDF Energy over pay and contracts after 'draconian cuts'.
However, EDF Energy have told the 'News' that they are not aware of any ballot notifications and are 'actively engaging' with trade union partners.
Contingencies would likely be put in place to keep the electricity grid running if strikes were to go ahead.
GMB says it has informed the Scottish Government about the implications of industrial action at the two sites, which employ a total of 1500 workers
Gary Smith, the union's Scottish Secretary, said: “Industrial action at Hunterston B and Torness could have profound implications for electricity generation and supply across Scotland, but we have been left with little choice than to take on EDF over these draconian cuts. Each year two of Hunterston B and Torness's four reactors must be shut down by law for two months at a time to enable safety checks, when staff may be required at short notice to come in. Enhanced pay rates were negotiated for these periods, which the GMB claims EDF wants to renege on.
Mr Smith added: “During these periods staff become fully available, work flexibly to accommodate the employer’s requirements and receive enhanced rates in return.
"The outage [shut down] rates were negotiated by trade unions because this is an intensive period of work that places significant demands on staff across the UK’s nuclear fleet and it is ludicrous that a hugely profitable multi-national like EDF is trying to break this agreement..
"Outages are a statutory requirement, a safety-critical process delivering the maintenance of our nuclear reactors.
"During these periods staff become fully available, work flexibly to accommodate the employer's requirements and receive enhanced rates in return."
The dispute centres on EDF's plans to cut a long-standing agreement about pay and contracts during outages.
GMB intends to launch a consultative ballot on industrial action this week.
EDF Energy said it had not formally been made aware of the union's plans.
A spokesperson said: “We’re sharing open and constructive dialogue in a period where costs are going up and income from electricity generation is going down and have been having productive conversations."