The SNP has refused to reveal whether it has taken any legal advice about the possibility of Scotland having to reapply for EU membership if it gains independence.
In a letter released by Labour, External Affairs Secretary Fiona Hyslop said it would be "contrary to the public interest" to reveal details about what, if any, advice had been taken by the party.
The SNP has however rejected suggestions that Scotland would be forced to reapply to join the EU after independence.
The administration defended its position after a report by the House of Commons Library.
The publication sets out three likely options for post-independence Scotland and what would remain of the UK.
Options include both parts continuing in the EU after separation; Scotland being forced to re-apply while the rest of the UK continues; and "dissolution", where both parts would be forced to re-apply.
The paper sparked fresh calls for the SNP to spell out exactly what would happen and what advice ministers have been given.
In the letter, Ms Hyslop wrote: "We consider that to reveal whether or not the information you have requested exists, or is held by the Scottish Government, would be contrary to the public interest."
But a spokesman for First Minister Alex Salmond said the position is "crystal clear".
The spokesman added: "Scotland is already an integral part of the EU - and as an independent state will be in exactly the same position as the rest of the UK as a successor state.
"Legal, constitutional and European experts have all confirmed that an independent Scotland would continue in EU membership.
"And how could it be otherwise, when Scotland has the lion's share of the EU's energy reserves, including oil and renewables?
"The fact is that the last major EU expansion in 2004 saw 10 new countries join - six of them smaller than Scotland, and six of which have become independent since 1990.
"Scotland would not be a new part of the EU and the issue of the euro would be decided by a referendum of the people of Scotland, and only when the economic circumstances were right - until such a point, an independent Scotland will retain sterling as at present."
The Commons report concedes there is "no clear answer" to Scotland's continued role in the EU.
It also refers to what happened when Czechoslovakia split into two countries.
"If instead it is considered that a state is entirely dissolved and new states are created, both or all such states will have to apply afresh for membership of international organisations," the report states.
Shadow Scottish Secretary Margaret Curran MP said: "Under the SNP plan there is a real risk that Scotland could end up out of the UK and out of Europe, or in Europe but obliged to immediately adopt the euro. Both scenarios would be a disaster for the Scottish economy and Scottish exports."
Scottish Conservative constitution spokesman David McLetchie MSP said: "Alex Salmond and the SNP may dispute the conclusions of this report but that does not relieve them of the duty to provide definitive answers to the questions it raises about our relationship with the EU and the euro.
"Of course, it could be that Alex Salmond is too feart to ask the EU these questions as he knows Scots won't like the answers."
A Scottish Government spokesman said: "The FOI response to which the letter relates was released and reported in August.
"The position is clear - an independent Scotland will continue in membership of the EU.
"On the general and separate issue of legal advice on any matter, it is the practice of successive governments, reflected in the Scottish Government ministerial code, that the fact and content of legal advice is not disclosed."