Jeremy Corbyn has been criticised by several of his MPs for his leadership on anti-Semitism and Brexit during a “heated” meeting in Parliament.
Marie Rimmer told him people “who have worked with you for ages” were turning away while Jess Phillips said those “in the cult of Corbyn” were protected.
Veteran MP Margaret Hodge criticised the choice of Lisa Forbes as Labour’s Peterborough by-election candidate.
Ms Forbes apologised to MPs for liking an anti-Semitic post on social media.
The new MP, who won Thursday’s by-election by 683 votes, caused controversy during the campaign when she appeared to endorse a post on Facebook which said Theresa May had a “Zionist slave masters agenda”.
Jewish Labour groups have called for Ms Forbes, who will take her seat in Parliament on Monday, to have the whip suspended.
Addressing the parliamentary party for the first time since Labour’s disappointing performance in last month’s European elections, Mr Corbyn thanked all those MPs who contributed to Labour’s successful campaign in Peterborough.
But he faced criticism over the message that Ms Forbes’ victory sent about the party’s commitment to eradicate anti-Semitism from its ranks.
Mrs Hodge said she could “not tolerate” anti-Semitism of any kind within the parliamentary Labour Party while Ruth Smeeth accused Mr Corbyn of “allowing institutional anti-Jewish racism on your watch”.
The party is currently being investigated by the Equalities and Human Rights Commission over claims it discriminated against Jewish members.
Mr Corbyn told the meeting that Labour “must be, is, and always will be anti-racist in any form, including anti-Semitism” – and Ms Forbes must be treated “properly”.
Labour has suggested Ms Forbes made a “genuine mistake” by liking a video expressing solidarity with the victims of March’s terror attacks on mosques in Christchurch “without reading the accompanying text, which Facebook users know is an easy thing to do”.
Mr Corbyn also came under fire over Brexit with Peter Kyle, a strong supporter of another referendum, questioning whether the Labour leader had any plan to get the country and party out of the Brexit “mire”.
And Meg Hillier said the leadership was wrong to demote Emily Thornberry from her traditional role deputising for Mr Corbyn at last week’s Prime Minister’s Questions.
Ms Thornberry was replaced by Rebecca Long-Bailey after she said Labour’s third place in the Euro elections boosted the case for another referendum – an outcome that Mr Corbyn continues to distance himself from and has said is “some way off”.
A number of MPs expressed concerns that it had now become “normalised” for Labour voters to back other parties over Brexit.
Mrs Rimmer, previously regarded as being loyal to Mr Corbyn, suggested she had struggled herself to vote for Labour in the elections.
After the meeting, a spokesman for Mr Corbyn said there were strong feelings about Brexit and the shadow cabinet would discuss Labour’s “evolving” position on Tuesday.
“The PLP [the parliamentary Labour Party] is generally quite a robust meeting,” he said. “The PLP is very passionate about lots of issues not just about Brexit. That’s what we would expect.”