The First Minister's calling on the UK government to intervene in talks over Longannet's future.
Scottish Power is expected to have around a month to secure an agreement with the National Grid over how much it pays to connect to the system.
260 jobs are at risk if the plant shuts five years early over high operating costs.
Scottish Energy Minister Fergus Ewing said:
“I welcome that the Prime Minister says he is taking the issue of security of electricity supply seriously, but from that assurance must then flow action to assess the negative impact of UK energy policy and regulatory regime on Scottish generation.
“I am particularly concerned that he seems relaxed that his energy policies are contributing to the potential premature closure of Longannet power station in Fife.
“Given that his colleagues in Scottish Conservatives have recognised the discrimination against Longannet and the need for secure energy generation to continue in Scotland, the First Minister has now written back to the Prime Minister calling on him to increase the transparency around the effect of UK energy policy in Scotland.
“With hundreds of direct jobs at risk at Longannet, and the viability of future thermal plants also undermined by transmission charging that is surely the least he can do.”
Tom Greatrex, Scottish Labour’s Shadow Energy Minister, and MP for Rutherglen and Hamilton West said:
“The ongoing threat to Longannet brings sharply into focus the increasingly imbalanced energy supply we have in Scotland, and why we need to ensure we have a balanced energy mix for the future.
“Already we are increasingly reliant on importing power from England to keep the lights on in Scotland when the wind isn’t blowing – without Longannet that situation will become even starker. That is why it is important for National Grid and Scottish Power to continue to negotiate.
“Fergus Ewing is either intentionally obfuscating or genuinely ignorant of the fact that it is the SNP’s policy which has driven the increasing imbalance in our energy mix, leaving us so reliant on the rest of the UK for power at times of high demand and low renewable generation.
“While the delay in the implementation of Project Transmit has been frustrating, the SNP’s synthetic outrage over transmission charging is a red-herring – a new regime is being introduced next year, which the Nationalists claim to support. Until recently, the SNP were advocating a postage-stamp model of transmission charging that would add £7bn to the consumer bill.”