Nicola Sturgeon is seeking urgent assurances from David Cameron after reports of a rule change allowing the UK Government's electronic surveillance agency to monitor the communications of MSPs and other devolved representatives.
The First Minister has written to the Prime Minister calling on him to clarify whether communications from MSPs have been intercepted by the intelligence agencies following revelations published in the Daily Record newspaper.
Labour MP Ian Murray has tabled a series of Parliamentary questions in the House of Commons in response to the "outrageous" report about an apparent change to guidelines at Government Communications Headquarters (GCHQ).
The newspaper reported that MSPs - as well as MEPs and members of the Welsh and Northern Irish assemblies - have been excluded from the Wilson doctrine, introduced in 1966 under former Labour prime minister Harold Wilson to ban the tapping of UK MPs' and peers' phones and later extended to cover emails.
Although the doctrine was never officially extended to cover the Scottish Parliament and Welsh and Northern Ireland assemblies when they were set up, devolved representatives had previously been treated in the same way.
According to documents obtained and printed by the newspaper, guidelines in place before March state: "As a matter of policy GCHQ applies the principles of the Wilson doctrine to Members of the House of Commons, Members of the House of Lords, UK MEPs, and members of the Scottish, Welsh and Northern Irish assemblies."
In contrast, new guidelines issued last month say: "The doctrine does not apply to... the interception of communications of Members of the European Parliament or devolved assemblies."
Ms Sturgeon said the Scottish Government had not been consulted on the apparent change and urged Mr Cameron to confirm that the Wilson doctrine remains in place in Scotland.
She wrote: "I am sure you will agree with me that, excepting truly exceptional circumstances involving national security, the confidentiality of communications between parliamentarians and their constituents is of the utmost importance.
"I am sure you will also agree that it is just as important for MSPs as it is for MPs. This principle of confidentiality is what the 'Wilson doctrine' was introduced to protect.
"You will therefore understand my concern at suggestions in the Daily Record and elsewhere - reportedly supported by documentation shown to the Investigatory Powers Tribunal - that, while GCHQ had been applying the Wilson doctrine to the communications of MSPs, that is no longer the case."
The First Minister called on the Prime Minister to clarify whether there had in fact been a change in policy and if so when the decision was taken and who was aware of it.
She also sought assurances that if the reports are true, the policy change will be reversed and MSPs will be treated equally to MPs.
Scottish Labour's acting leader Iain Gray MSP said: "It is utterly unacceptable for the communications between devolved representatives across the UK and their constituents to be monitored by GCHQ.
"There needs to be full transparency from the UK Government on this. We need to know urgently who decided on this major rule change and when.
"For the rules on spying on elected representatives across the UK to change without any sort of public scrutiny or accountability is a democratic outrage.
"We also need to know from each of the devolved administrations what, if anything, they knew about this change."