Deputy Labour leader Tom Watson has survived a move to oust him by abolishing his post.
The proposal was heard at the party’s National Executive Committee on Friday but failed to get the two-thirds majority needed.
It is understood that it was proposed by Jon Lansman, founder of Labour grassroots group Momentum.
A fresh move will be made on Saturday at the party’s conference and is expected to be successful.
Momentum was set up to support Jeremy Corbyn’s leadership of the Labour Party.
Mr Watson has been at odds with Mr Corbyn over Labour’s stance on Brexit.
He wants another public vote on the UK’s membership of the EU before any general election, but Mr Corbyn has said an election should come first.
The party leader has refused to say which side he might back in a future Brexit referendum under a Labour government.
A Momentum source told the BBC: “We just can’t afford to go into an election with a deputy leader set on wrecking Labour’s chances.
“Labour members overwhelmingly want a deputy leadership election, but our outdated rulebook won’t let it happen.”
The NEC will vote again on abolishing Mr Watson’s post at the party’s annual conference at 10:00 BST on Saturday.
Sources told BBC political editor Laura Kuenssberg they expected the vote to be passed.
There will then be a vote on the conference floor in the afternoon, where it is expected the bid to be approved, ousting Mr Watson.
BBC political reporter Jessica Parker said Mr Watson’s supporters were “not overly optimistic” that he will win that Saturday’s vote.
Labour MP Wes Streeting said in a Twitter post the move to remove Mr Watson “isn’t just outrageous, it’s self destructive”.
“Labour Conference this week needs to put the Party on a general election footing – talking to the country about our vision for Britain,” he wrote.