Jeremy Corbyn’s inner circle has been accused of interfering in the outcome of anti-Semitism cases to reduce the sanction imposed.
Labour MP Margaret Hodge claimed Corbyn had either misled her or been misled himself about the extent of his team’s involvement in cases.
She accused Corbyn of promising a “zero tolerance approach” but did not demonstrate that if the cases involved his “mates”.
Hodge, who is Jewish, has a history of clashes with Corbyn.
Labour insisted that it was “categorically untrue” to suggest that staff in the leader’s office overturned recommendations in cases.
Hodge has written to Corbyn setting out her concerns, which follow an Observer report at the weekend about the process followed in certain anti-Semitism cases.
Tom Watson, Labour’s deputy leader, is due to meet Corbyn today to discuss anti-Semitism in the party.
Hodge, the MP for Barking and Dagenham, told BBC Radio 4’s Today programme she had been given “absolute, copper-bottomed undertakings” by Corbyn that there was “no interference in the complaints process by his inner circle”.
She added: “What we then discover from the Observer on Sunday, and I have seen further emails, is that a whole number of his top team – not just one person, lots of them – are involved in decisions around individual complaints and what they do is they interfere and they lower the sanctions so people aren’t suspended, they are just given a warning letter.
“What is so awful about this is that Jeremy always proclaims zero tolerance of anti-Semitism. When it comes to the actual cases, if they are his mates he doesn’t demonstrate zero tolerance.
“He claims no political interference in these cases, I have now seen so much evidence there is definitely political interference.
“So trust in him has gone. Misleading me, or himself being misled, really undermines my trust for him.”
A Labour Party spokesman said: “Since becoming general secretary, Jennie Formby has made procedures for dealing with complaints about anti-Semitism more robust.
“Staff who work on disciplinary matters have always led on investigations and recommendations on individual cases.
“Any suggestion that staff in the Leaders’ Office overturned recommendations on individual cases is categorically untrue.”
But Hodge said: “I have got evidence that under the new general secretary of the Labour Party those very close to Jeremy Corbyn, his inner circle, were involved in discussing cases of terrible anti-Semitic abuse and in lowering how those people were dealt with.”
She also questioned the plan for former lord chancellor Lord Falconer to be brought in to examine the issue, saying she did not believe he was independent and it could be a repeat of Baroness Chakrabarti’s inquiry, which critics branded a whitewash.
Hodge said Lord Falconer had repeatedly urged her to apologise following a heated clash with Corbyn last year in which she called the Labour leader a “racist and anti-Semite”.
She said she was “absolutely bombarded by telephone calls from Charlie Falconer, they were not about the rights and wrongs of the case, they were all about trying to force me to give an apology – he is not independent”.
“We need somebody totally outside the Labour Party otherwise this becomes another Chakrabarti fiasco,” Hodge said.
Hodge’s intervention follows a stormy meeting of the Parliamentary Labour Party on Monday night.
Some Labour MPs reacted angrily to the appointment of a staff member from Corbyn’s office to the party unit dealing with complaints of anti-Semitism.