The figures, from financial accounts revealed ahead of the party’s spring conference in Dundee this weekend, show donations fell by almost 77 per cent in 2018 compared with the year before.
They totalled just £35,555 compared to £152,690 in 2017, contributing to a 65 per cent drop in income that drove the party £32,452 into the red at the end of 2018.
The party said the decline could be explained by the fact there was no election campaign last year.
But insiders said that donors were “deserting in their droves” due to the party’s Brexit stance.
Despite campaigning for Remain ahead of the 2016 referendum, both Jeremy Corbyn and Scottish Labour’s leader Richard Leonard have said that the result of the vote should be respected.
Mr Leonard has come in for particular criticism for following Mr Corbyn’s lead on Brexit, given that 62 per cent of the Scots who voted wanted to stay in the EU.
A week ago he said he would prefer a negotiated Brexit to a second referendum on the issue – but added that he would campaign for Remain again if there was another vote.
A Labour source said: “Just like our members, donors are deserting in their droves.
“The party’s position on Brexit is failing Labour’s core support, of which there is precious little left.
“When the party has nothing pro-business to say and fails to rise to meet the biggest issue of our times, it is little wonder donors are keeping their hands firmly in their pockets.”
However, another party source denied this, saying their comparatively weaker financial position was “just a natural consequence of being on an election footing outside of an election period”.
A party spokesman added: “Unlike the Tories, we are not a party backed by and for big businesses and millionaires. We are proud of being a people-powered movement funded by lots of smaller donations and trade union members.
“This was the first year since 2013 that Scottish Labour hadn’t been fighting either an election or a referendum campaign and our membership has almost doubled since the independence referendum.
“Since 2017, we’ve been on an election footing because we need to get rid of this shambolic and cruel Tory Government, and when an election is finally called we will be ready to fight and win.”