Two of Labour's most senior figures have clashed over how to handle anti-Semitism within the party.
General secretary Jennie Formby accused deputy leader Tom Watson of "completely unacceptable" behaviour for asking that complaints about anti-Semitism be forwarded to him for monitoring.
She said his approach would "undermine" and "pollute" existing party processes.
Mr Watson stood by his request, saying "opacity and delay" by the party had led to "a complete loss of trust".
The Labour Party has been dealing with complaints of anti-Semitism over the last two years.
Mr Watson's original intervention came after nine MPs quit the Labour Party last month citing the party's failure to tackle anti-Semitism as one of the reasons.
Mr Watson emailed all Labour MPs and peers telling them he would be "logging and monitoring" complaints of anti-Semitic abuse and bullying.
Ms Formby then wrote to him, copying in all Labour parliamentarians.
She told him: "It is absolutely inappropriate for you to set up a vague parallel complaints monitoring system."
Ms Formby said that he and the party had "very strict responsibilities" to safeguard members' data under GPDR and data protection laws and asked for complaints not to be sent to Mr Watson "or any unauthorised individual".
She added: "Furthermore, you will undermine the work that my staff and I are doing and will confuse and pollute the existing formal process, compromising it and slowing it down."
Mr Watson responded: "The constant concern of those complaining about anti-Semitism in our party is that there is no transparency about the process.
"Too often those who have suffered anti-Semitic abuse have not heard anything about the outcome of their complaint.
"It is my responsibility as deputy leader of the Labour Party to ensure people have confidence in our complaints system and our ability to deal transparently with the scourge of anti-Semitism.
"I will continue to do everything I can to achieve that."
Catherine McKinnell, Labour MP for Newcastle upon Tyne, told BBC Radio 4's Today programme: "I, for one, have hugely welcomed Tom's intervention in this."
She said the current complaints system had a "huge amount of trust to rebuild", and that too many complaints "just seem to disappear".
"Nobody knows what the outcome of the complaint has been, nobody knows what the process has been," Ms McKinnell said, adding: "The figures don't match up. So I think there does need to be some oversight."
Jewish members 'distressed'
It comes as members in Diane Abbott's Hackney North constituency issued a motion against MPs who "slander the party" by claiming it is "institutionally anti-Semitic".
Labour's Stella Creasy, who represents the neighbouring London constituency of Walthamstow, said the motion was "disgraceful" and called on Ms Formby to investigate the local party.
She tweeted: "What on earth is going on... that such a motion can be put forward?"
Sheffield Hallam members backed a similar motion and called for the reinstatement of MP Chris Williamson, who was suspended by the party last week for saying Labour had "given too much ground" in the face of criticism over anti-Semitism.
Brent councillor Neil Nerva, a member of the Jewish Labour Movement, said colleagues at the meeting in Hackney North had said shadow home secretary Ms Abbott was present.
He said Jewish members were "distressed" that the MP did not comment on the motion being voted on, adding: "Now to me, that is becoming a bystander. I don't know whether Diane felt intimidated about standing up and saying what was being done."
Ms Abbott has not responded to questions about the meeting.