Almost a third of Newham councillors have signed a complaint against the borough's mayor, Rokhsana Fiaz.
The Recorder has seen the complaint, signed by 18 councillors, that was made to London Labour in July 2020.
They allege Ms Fiaz "constantly picked on colleagues", humiliated them in front of others and "regularly treated people unfairly" over the two years prior.
Ms Fiaz did not respond to a request for comment, nor did Newham Council, Newham Labour or the national Labour party, while London Labour declined to comment.
However, Newham Council told one of the signatories that it is not a matter for the local authority, but should be dealt with by the party.
Cllr Pat Murphy said he had quit the Labour group on Newham Council because he felt the party had not investigated the allegations.
The Royal Docks ward representative said London Labour had not responded to the complaint.
"There has been nothing other than silence from the party," he added.
The complaint alleges: "Her (Ms Fiaz's) behaviour has created a hostile, intimidating and oppressive environment within the group during meetings, causing members to feel unable to freely express their views on issues of concern to them.
"Ms Fiaz's behaviour is making members feel afraid and unable and unwilling to question and hold her administration to scrutiny within private meetings of the group.
"The fear of being bullied and harassed by Ms Fiaz in both public and private is intolerable."
%image(15254934, type="article-full", alt="Cllr Pat Murphy has resigned as a member of the Labour group on Newham Council")
The complaint adds that requests from the councillors for Ms Fiaz to stop the alleged "untenable" behaviour had "not been heeded".
Cllr Murphy said he thinks Ms Fiaz is "completely unfit for office".
For him, the selection of Ms Fiaz as Labour's mayoral candidate for Newham in the upcoming May elections was key in the timing of his resignation.
Cllr Quintin Peppiatt, who spent 15 years as a cabinet member for children and young people until Ms Fiaz's election in 2018, has also left the Labour group.
He and another councillor complained to Labour in November 2020 alleging Ms Fiaz had failed to tackle alleged antisemitism in Newham Labour, but he said neither Ms Fiaz or Labour responded.
%image(15254939, type="article-full", alt="Cllr Quintin Peppiatt said Ms Fiaz's selection as Labour's candidate to be Newham mayor was the "final straw" leading to his resignation from the group")
Like Cllr Murphy, Cllr Peppiatt said the "final straw" was Ms Fiaz's selection as Labour's candidate for mayor without a resolution to the complaint.
He told the Recorder: "I've been a member of the Labour Party for 40 years. Personally it's been a very hard decision. But you have to make decisions based on what you think is right.
"They may dismiss it [the complaint]. That's up to them. But what I found unacceptable is they hadn't even replied to us or made it transparent.
"I have no confidence in the Labour Party taking this issue at all seriously.
"In an ideal world, I want to stay in the Labour Party but I didn't feel I could do that with the lack of action on this matter."
Cllr Peppiatt, a reverend, said he also sent the complaint to Newham Council, but was told it was a party matter.
He claimed that he received a letter to say he had been excluded from Labour in three days - compared to more than a year without a response to his complaint.
Additionally, he also cited the closure of Newham City Farm as another reason for his resignation, saying he "fundamentally disagreed" with the decision to cut funding.
Both councillors will be independents until the May election, with both confirming they will not be seeking re-election.
Cllr Peppiatt said: "After 25 years, it's right for me to step down. I've done my bit.
"I'm very proud of my record and it's time to go."
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