Jeremy Corbyn has been accused by Labour leadership rival Owen Smith of consistently undermining his colleagues as the pair prepare to square up in a prime time television clash.
The party leader is "more interested in deepening the divides within the party than winning elections", according to his challenger.
Mr Corbyn has tolerated abuse in the party and his team has taken part in attacking staff, Mr Smith claimed as he promised to "bring an end to abuse and intimidation once and for all".
A dossier setting out why the party leader is the "disunity" candidate has been compiled by the former frontbencher's campaign team.
Mr Corbyn's team described it as a "dodgy" collection of rehashed claims that shows Mr Smith's desperation.
But Mr Smith insisted the leader has "repeatedly undermined" Labour staff.
His dossier states: "Jeremy Corbyn says he won't tolerate abuse but he has repeatedly downplayed or denied abuse was happening, told people to ignore it, criticised actions to tackle it and his campaign and those in his inner circle have actively taken part in it.
"Jeremy Corbyn says he condemns attacks on Labour Party staff, saying they should not be used as a 'political football'. But he has repeatedly undermined Labour Party staff, his inner circle have actively attacked them and those around him are reportedly plotting to have them sacked.
"Jeremy Corbyn says that he doesn't support a rule change to deselect MPs. But he has himself warned of de-selections of Labour MPs."
Mr Corbyn and Mr Smith are taking part in a BBC One's Question Time hustings special live from Oldham.
The Labour leader is favourite to win the leadership contest despite losing the support of the overwhelming majority of his MPs.
Mr Smith said: "Jeremy is the disunity candidate in this contest. Labour has become increasingly divided on Jeremy's watch and the people around him, like John McDonnell, appear content with seeing the party split.
"By failing to act against abuse, attacking party staff and the NEC (National Executive Committee) and encouraging talk of de-selection, Jeremy has shown that he is both unwilling and unable to act as a unifying figure.
"That's not the leadership the Labour Party needs - it's not leadership at all.
"He says he wants to build bridges, but the truth is he appears more interested in deepening the divides within the party than winning elections.
"If we are to defeat the Tories in 2020 then we need to be united against them, not divided against ourselves.
"As Labour leader I would heal the divides within Labour and take the fight back to the Tories.
"I would build a shadow cabinet that reflects every wing of our movement, empower ordinary members to give them a binding vote on policy issues, and bring an end to abuse and intimidation once and for all."
A Jeremy For Labour spokeswoman said: "Smith's dodgy dossier is a new low in his increasingly desperate and negative campaign.
"He has consistently talked down Labour rather than offer a convincing vision of the future including joining forces with Theresa May to attack the Labour leader on the morning of PMQs.
"Smith's latest helping of 'Project Fear' only recycles allegations he knows to be false or misleading, but it won't wash with Labour members and supporters who want open, honest politics.
"Our campaign has set out a positive vision to rebuild and transform Britain.
"In contrast, Owen Smith has shown himself yet again to be the real 'disunity candidate', which is why a recent YouGov poll suggests he is 24 points behind in the contest, and Jeremy has support across every section of our party."
Meanwhile, Mr Corbyn is also likely to face questions about his stance on whether Britain should stay in the European single market after Brexit.
The Labour leader came under fire after a senior aide suggested he might rule out full membership of the European single market unless Britain can negotiate exemptions from key EU rules.
That prompted Mr Corbyn's team to stress that he backed "full access" to the single market for goods and services but opposed certain directives linked to it, such as state aid rules and requirements to deregulate and privatise public services.