In a sign of growing national interest in the issue, senior members of the Scottish Trades Union Congress (STUC) will brief the TUC general council in London on December 11 about the referendum and the potential impact of the ballot on the union movement north and south of the Border.
The discussion was called by the TUC and its outgoing general secretary Brendan Barber is due to take part, along with his successor Frances O'Grady.
Union general secretaries including Len McCluskey of Unite, Dave Prentis of Unison and Mark Serwotka of the Public and Commercial Services union (PCS) are also expected to be involved, but have yet to be confirmed.
Awkwardly for Labour, which insists voters will reject independence, next month's meeting marks the start of a contingency planning exercise by the unions in case voters do support separation.
The exercise could also see major unions backing Labour's opposition to independence, despite an instinctive reluctance to align with the Tories and LibDems on an issue.
Grahame Smith, STUC general secretary, said that the organisation had yet to take a position on independence, but could do so at its congress in April 2013 or 2014.
He said it was a genuinely open question what the STUC's stance might be, and it would be wrong to assume it would automatically oppose independence because of its links with Labour.
The STUC, which represents 630,000 workers, is currently consulting on what powers Holyrood needs to create a fairer Scotland by tackling poverty and inequality and reforming employment law. Smith said: "We have met with the Labour leadership and the SNP.
"We are not rushing to take a decision. We have the time to do that."
The London meeting comes as both the Yes and No camps in the referendum debate step up their wooing of the unions, whose support could provide vital finance and organisational support.
Union sources say Alex Salmond has been going out of his way to court the movement in recent months, offering an input to the Scottish Government white paper on independence which is due out in 12 months.
Securing the support of even a handful of unions would be a publicity coup for Salmond, as he could claim resistance to independence among traditional Labour voters was crumbling.
However, Scottish unions have so far been unwilling to survey their members on independence, as they know it would be hugely divisive, both for the membership and for their own leadership.
Only one union has so far taken a stand on independence, with Aslef opposed.
Paul Nowak, TUC head of organisation, said of the London meeting: "We want to make sure unions and their members are engaged in a wide debate which starts from our shared aspiration to create a fairer, better society in Scotland and indeed across the whole of the British Isles."