The European Commission, the EU's governing body, will only comment on an independent Scotland's prospective EU status if it is approached by a current EU member state.
The Scottish Government is not entitled to seek its own opinion as it is a devolved administration.
Only the UK Government is permitted to approach the EC, but it has made clear it will not "pre-negotiate" the terms of independence ahead of the referendum.
Now SNP MEP Alyn Smith has written to Prime Minister David Cameron, Scottish Secretary Michael Moore and Deputy First Minister Nicola Sturgeon urging them to make a joint approach to the EC.
He also asked Tory MEP Struan Stevenson, Labour MEP Catherine Stihler and Liberal Democrat MSP Liam McArthur to add their names to the letter at a debate at Edinburgh University this evening.
None of the MEPs indicated whether they would sign Mr Smith's letter at the debate.
Mr McArthur echoed the comments of his Liberal Democrat colleague Michael Moore, saying the SNP is "trying to hang a picture that has not been painted".