The former leader of Scottish Labour has launched an attack on her successor just days before the party's conference.
Kezia Dugdale strongly criticised Richard Leonard's approach to Brexit in a letter that that was later leaked.
She also accused him of "censoring" two of the party's MEPs over their support for another referendum on EU membership.
A Labour source said this had been the result of a "misunderstanding".
And he said Mr Leonard had written to the two MEPs - Catherine Stihler and David Martin - to apologise.
The party's conference in Dundee begins on Friday and lasts until Sunday.
In her letter, Ms Dugdale said she wanted to "formally complain" to Mr Leonard about the way in which Ms Stihler and Mr Martin had been treated ahead of the conference.
She also claimed Ms Stihler's section in the conference guide had originally included a statement in support of a so-called People's Vote on Brexit which had been changed without her consent.
Ms Dugdale wrote: "From what I can see from the agenda, there is no formal opportunity for them to speak or indeed a formal item to thank them for their combined 55 years of electoral service to the party.
"If that wasn't bad enough, I was shocked to discover from Catherine that her statement in the conference guide had been amended without her consent.
"When that was challenged, she was told it was on your direction and that you had the final say on what was printed."
Ms Dugdale, who has been a prominent campaigner for another referendum on Brexit, claimed the section had originally said: "Brexit is a tragedy for our country and for the workers and communities that Labour represents.
"That's why David and Catherine fully support a People's Vote with the option to remain in the EU."
However, according to Ms Dugdale, the section was replaced with: "The complete mess the Tories have made of Brexit means they are putting Scottish people's jobs and our industries at risk. Labour will always put them first."
Ms Dugdale said changing the section without Ms Stihler's permission was "wholly inappropriate", adding: "I can't possibly understand why you would seek to censor her final words to party members, especially since what she states is party policy and has been since last September."
A Labour source told BBC Scotland: "This was a genuine misunderstanding and Richard has written to Catherine and David to apologise."
Mr Leonard was also criticised in the email for his stance on Brexit, with Ms Dugdale expressing her disappointment that his support for holding a People's Vote had not come sooner.
She wrote: "You know that I've found the party's position on Brexit and a second EU referendum disappointing for some time.
"As I said at group last week and repeatedly over the past few months, I don't believe there is such a thing as a good Brexit or indeed a 'jobs first Brexit'.
"The move towards supporting a People's Vote is a welcome one, but it should have happened much, much earlier. I note from your roundtable with journalists last week that you'd sooner we left the EU than give people a final say.
"That's disappointing for the many party members who fervently back a final say and indeed all of our voters who are now a bit lost for a home."
Mr Leonard is a close ally of Labour leader Jeremy Corbyn, who had previously resisted pressure from Remain supporters in his own party to get behind another referendum, insisting he preferred to force a general election.
But Mr Corbyn announced a change of heart last month, telling his MPs: "One way or another, we will do everything in our power to prevent no deal and oppose a damaging Tory Brexit based on Theresa May's overwhelmingly rejected deal.
"That's why, in line with our conference policy, we are committed to also putting forward or supporting an amendment in favour of a public vote to prevent a damaging Tory Brexit being forced on the country."
Mr Leonard later told BBC Scotland he backed the move, saying it could be the only way to break the deadlock over Brexit at Westminster.
He also said he was "disappointed" that Labour's investigation into claims of Islamophobia against a Dumfries and Galloway councillor was taking so long.
Jim Dempster was suspended by Labour in March of last year after admitting telling transport officials that "no-one would have seen [then-transport minister Humza Yousaf] under his burka".
Mr Yousaf told BBC Scotland he was hurt that the case had still not been dealt with almost a year after it was referred to Labour's national disciplinary body in London.
But Mr Leonard said: "The case is being dealt with through due process. I'm disappointed that it's taking as long as it has - the person involved in the complaint is still suspended from the Labour Party and I hope this will be resolved very quickly indeed".
Mr Dempster apologised to Mr Yousaf at the time, saying he was "thoroughly ashamed and embarrassed" by the comments he had made, and that "my ignorance is totally inexcusable."