Two Nationalist MSPs have declared that they will not support John Swinney in a leadership ballot because of his position on independence.
Mr Swinney has been criticised over a key policy
Bruce McFee and Adam Ingram accused the SNP leader of watering down the party's commitment to independence during this year's Holyrood elections.
Mr McFee said he would abstain from the leadership vote at the party's conference in Inverness next week.
Mr Ingram said he planned to vote for Dr Bill Wilson, Mr Swinney's challenger.
The Nationalist MSPs said Mr Swinney's position on independence had confused the voters and had led to a disappointing result for the party in May.
In the 2001 General Election and in this year's Holyrood campaign, Mr Swinney said the party would promise a referendum on independence after an SNP election victory.
This was a shift from the previous policy whereby winning an election would be considered a sufficient mandate.
Mr McFee, a list MSP for the West of Scotland, said: " I really can no longer endorse the direction that the leadership is taking.
"Under John Swinney's leadership we're now told that the referendum would be in year two or year three of the SNP forming a government in Edinburgh."
Adam Ingram will vote against the leader
"What is very clear is that this policy has been used by the leadership as a way of watering down the independence message, to say to people 'you can vote SNP without believing a word we say about independence'."
South of Scotland list MSP Mr Ingram told Scottish Television: "We spent far too much time at Scottish parliamentary elections telling people that voting SNP was not a vote for independence in terms of having a referendum."
The MSP said the strategy had been to "park" independence until a referendum, which "totally confused our supporters in particular, and we lost a lot of our core voters".
Mr McFee said the leadership had not taken into account fears that efforts would be made by the British Government to "destabilise" an SNP administration prior to the referendum.
He said: "Let's be quite clear about this. The leadership have used this policy for a reason that the party never intended and that was to make it an independence-like policy so that they could back-pedal the independence policy and as a Nationalist I fundamentally disagree with doing that.
Swinney loyalist Fiona Hyslop was unperturbed by reports that about a third of the party would not support Mr Swinney.
The Lothians MSP said the result might reflect the ballot in 2000 when Mr Swinney beat Alex Neil in the leadership contest.
She said: "This isn't a surprise - it's the same vote as it was when the contest was last fought three years ago."