A prominent Scottish independence campaign group has begun a fundraising drive, saying it expects a second referendum to be called within weeks.
Business for Scotland said it was getting "back in full campaign mode" for a vote in 2018.
It said it expected a vote to be called for May or September next year.
First Minister Nicola Sturgeon has previously said a second referendum was "highly likely" following the Brexit vote.
Business for Scotland focused on the economic case for independence ahead of the 2014 vote in which Scots voted 55% to 45% to remain part of the UK.
Group founder Gordon MacIntyre-Kemp has emailed members to say "we are only weeks away" from a second referendum being called.
In his message to supporters, Mr MacIntyre-Kemp said: "Business for Scotland was a vital contributor to the growth of the Yes vote in 2014. We need your help to renew the business and economic case for independence and drive Yes support to the levels required to call and win Indyref2.
"We didn't go away, instead we have kept on campaigning for independence and we also campaigned for a Remain vote in the EU referendum.
"We are getting ready for Indyref2 in May or September 2018 and so we are back in full campaign mode."
The group aims to raise £15,000 and said it had already raised nearly a third of the target.
Prime Minister Theresa May said earlier in February that the question of Scottish independence was "settled" by the 2014 referendum.
The SNP, however, argues that since a majority in Scotland voted to Remain, this represents a material change in circumstances that could justify a second vote.
The party has put forward proposals to secure Scotland's access to the European single market but Nicola Sturgeon has warned time is running out to find agreement.
Former SNP leader Alex Salmond has suggested an announcement from Ms Sturgeon is very close, and he has predicted a referendum in autumn 2018.
Others within the pro-independence camp have, however, signalled a more cautious approach.
A recent opinion piece by Robin McAlpine, director of pro-independence think tank Common Weal, asked whether the debate on indyref2 was "a bit too Culloden", referring to the crushing defeat of Jacobite rebels by a government army in 1745.
Mr McAlpine, who favours a 2019 vote, wrote: "If you were to make a calm assessment of the moment when we are at our strongest and our opponents are at their weakest, would you pick 2018?"