A group of 39 Labour politicians have called on Jeremy Corbyn to suspend the party's former disputes chief amid the ongoing row over anti-Semitism.
In an open letter, MPs and peers called for Christine Shawcroft to be suspended from the National Executive Committee.
Ms Shawcroft had quit as head of Labour's disputes panel after she sent an email showing support for a council candidate accused of Holocaust denial.
It comes as Mr Corbyn faces continued pressure to tackle anti-Semitism.
The letter, which is signed by 39 Labour politicians, said it was "utterly wrong" and "highly offensive to the Jewish community" that Ms Shawcroft remained a member of the NEC, which is Labour's governing body.
The lead signatory of the letter, the MP Siobhain McDonagh, told the BBC the group felt "very strongly" about the issue and that she and her colleagues had been "shocked to the core".
Ms Shawcroft, who is a director of the pro-Corbyn Momentum group, quit as head of the party's disputes panel on Wednesday after it emerged she had sent an email opposing the suspension of council candidate Alan Bull.
Mr Bull had been due to stand in the May local elections but is accused of sharing an article on Facebook which claimed the Holocaust was a "hoax". He said he reposted the article for the purpose of debate and did not agree with it.
Ms Shawcroft said she had not been aware of the "abhorrent" online post and said she was "deeply sorry".
In the letter, seen by the BBC on Thursday night, the Labour figures urged Mr Corbyn to take an "initial step" in honouring his commitment to tackle anti-Semitism.
The BBC understands Mr Corbyn intends to announce a speeding-up of the party's disciplinary procedures.
He has repeatedly condemned anti-Semitism, particularly in the past week following fresh accusations of anti-Jewish prejudice after it emerged he sent an apparently supportive message to the creator of an allegedly anti-Semitic mural in 2012.
The remarks led to a protest outside Parliament, organised by the Board of Deputies of British Jews and Jewish Leadership Council and attended by several Labour MPs, calling on Mr Corbyn to "root out" anti-Semitism in the party.
Mr Corbyn previously acknowledged anti-Semitism had surfaced within Labour, promised to deal with allegations of abuse more quickly and pledged to "rebuild" confidence in the party among the Jewish community.
According to the BBC's political correspondent Jonathan Blake, some of his supporters say the issue is being used to destabilise him.
Mr Corbyn's office has offered no response to the letter.