Video report by ITV News Political Correspondent Daniel Hewitt
More than 90 Labour MPs and peers - led by deputy leader Tom Watson - have issued a statement demanding Jeremy Corbyn withdraw the whip from Chris Williamson.
The statement said they cannot overstate the "depth and breadth of hurt and anger" at the readmission of the Derby North MP to the party following his suspension amid criticism of the way allegations of anti-Semitism were dealt with.
"It is clear to us that the Labour Party's disciplinary process remains mired by the appearance of political interference. This must stop. We need a truly independent process," the statement said.
"We call on Jeremy Corbyn to show leadership by asking for this inappropriate, offensive and reputationally damaging decision to be overturned and reviewed.
"Ultimately, it is for Jeremy Corbyn to decide whether Chris Williamson retains the Labour whip. He must remove it immediately if we are to stand any hope of persuading anyone that the Labour Party is taking anti-Semitism seriously."
However, asked this afternoon by ITV News if Labour's anti-Semitism allegations procedure is fit for purpose, Corbyn defended his party's response.
He said: ''We deal with anti-Semitism very, very seriously. There is no place for anti-Semitism in our society and obviously not in our party as well.
''Anyone that makes anti-semitic remarks can expect to be at the very least to be reprimanded, and if they are very serious, and they are engaged in anti-Semitic activity, then they are expelled from the party.''
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Asked if he was surprised by the decision to let Mr Williamson back into the party, Mr Corbyn said: ''I wasn't involved in the decision at all, it was an independent panel set up through the national executive, they examined the case and they decided to admit him back in allbeit with a reprimand.
''They went through the case, they interviewed him, they went through the case in great detail and the three of them on the panel made that decision.''
The statement comes after ITV News revealed the Jewish Labour Movement (JLM) will this week write to the Equality and Human Rights Commission (EHRC) asking them to investigate the decision to readmit Mr Williamson.
Mr Williamson has tweeted his "heartfelt thanks for the avalanche of goodwill messages from grassroots members" after his suspension from the party was lifted.
He was suspended in February after video footage showed him telling a meeting of the grassroots Momentum group that Labour's reaction to anti-Semitism allegations had led to the party being "demonised".
"I'd like to express my heartfelt thanks for the avalanche of goodwill messages from grassroots members," he wrote.
Mr Corbyn was questioned about the situation while campaigning in Hartlepool but again insisted he had nothing to do with the decision.
"It was an independent panel set up through the National Executive," he said, "they examined the case and they've decided to let him back in, albeit with a reprimand.
"They went through the case, they interviewed him and they went through the case in great detail. The three of them on the panel made that decision."
He said anyone who made an anti-Semitic remark "can expect to be at the very least reprimanded and, if they are very serious and they engage in anti-Semitic activity, then they are expelled from the party."