A Dundee-based Labour MSP has called for party leader Richard Leonard to quit.
Jenny Marra said the party was facing “catastrophe” if it does not change leadership ahead of the Holyrood election next May.
Her dramatic intervention came as the party’s justice spokesman, James Kelly, quit the shadow cabinet and also demanded Mr Leonard stand down.
Scottish Labour once dominated politics north of the border but has faced a series of humiliating setbacks in recent years.
Under the leadership of Mr Leonard, who took control in 2017, the party slumped to fifth at the European election in May last year and lost six of their seven seats at the general election in December.
Ms Marra, a list MSP for North East Scotland, told the Times: “If we do not change course now we risk catastrophe. Not just for the party but for all those who believe in and need a fairer, more equal Scotland.
“The reality is that you only have a short window in political leadership to make an impression on the public. After three years the party’s standing is getting worse rather than better.
“No one can say that Richard has not had opportunities to turn the situation around.
“Colleagues know that (Mr Leonard) is utterly committed to the party, the cause and he is liked by everyone.
“But the job we are asked to do by the party is not to let sentiment stop us from acting when all the evidence and our duty demands that we act.
“Richard is a stalwart of our party but he cannot lead us. That’s the unavoidable truth and change is our best hope.
“Richard’s leadership was tied from the start to the disaster of Jeremy Corbyn’s project.
“It remains so in the public’s view and they simply will not give the party a hearing as things stand.
“We need new energy, a new approach and to turn a new page.”
In his resignation letter, Mr Kelly said: “I have no confidence in your ability to shape the party’s message, strategy and organisation.
“I know that this is a view shared by other parliamentarians, party members and indeed many members of the public.”
But Mr Leonard insisted he would cling on to the leadership.
He said: “It is deeply disappointing that disgruntled MSPs who never supported my leadership would choose the day when the Scottish government finally accepted a Labour policy demand of ten years — for a National Care Service — to try and wage an internal war.”