A second Labour MP is facing possible suspension after criticising Labour's leadership over its new anti-Semitism code of conduct, the BBC understands.
Ian Austin, MP for Dudley North, is reportedly being investigated after a heated exchange with the party's chair.
He allegedly said the leadership "should be ashamed".
Labour's code of conduct was criticised for not using the full International Holocaust Remembrance Alliance (IHRA) definition of anti-Semitism.
It calls anti-Semitism "racism" that is "unacceptable in our party and in wider society", but it has not included all the IHRA's examples.
Mr Austin, who is a former adviser to Gordon Brown, reportedly told Labour's chair, Ian Lavery, that the failure to adopt the IHRA definition of anti-Semitism in full was "a disgrace".
According to the Observer, Mr Austin received a letter warning him he could face disciplinary action.
He told the newspaper: "I am angry about anti-Semitism and I am angry that the Labour party can't deal with it adequately."
Mr Austin has not yet spoken publicly on the investigation.
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Labour's executive committee approved its new code on anti-Semitism earlier this month following ongoing criticism of its handling of anti-Jewish discrimination and attitudes within its ranks.
The party says its own wording "expands on and contextualises" the IHRA definition and the examples which are not included are addressed elsewhere in the party's code.
The examples include requiring higher standards of behaviour from Israel than other nations and comparing contemporary Israeli policies to those of the Nazis.
After criticism of its definition, the party said it would "reopen development of the code" in consultation with Jewish groups.
The party's MPs will vote in September on whether to adopt the full IHRA wording after passing an emergency motion at a meeting on Monday night.
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He is the second Labour MP to face suspension over the issue, after the party launched a disciplinary inquiry into Labour veteran Margaret Hodge.
She reportedly swore at Jeremy Corbyn and called him an anti-Semite.
Earlier this week, the UK's three main Jewish newspapers united to publish the same front page, warning that a Corbyn-led government would pose an "existential threat to Jewish life".
Two senior members of Mr Corbyn's shadow cabinet have also suggested the controversial new code of conduct should be rewritten.
Shadow health secretary Jonathan Ashworth urged the party's ruling NEC to "reconsider" its decision and include the full definition.
Barry Gardiner, shadow international trade secretary, said it "would have been better" to adopt the IHRA definition in full.
Mr Corbyn has repeatedly said anti-Semitism is wrong and it will not be tolerated in the party.
What is the code of conduct row about?
Labour's code of conduct was drawn up earlier this month. It followed allegations of anti-Semitism within party ranks and came about after a 2016 inquiry chaired by barrister Shami Chakrabarti.
The code does reproduce the IHRA's "working definition" of anti-Semitism and lists behaviours likely to be regarded as anti-Semitic - but critics point out that it leaves out four examples provided by the IHRA definition:
- Accusing Jewish people of being more loyal to Israel than their home country
- Claiming that Israel's existence as a state is a racist endeavour
- Requiring higher standards of behaviour from Israel than other nations
- Comparing contemporary Israeli policies to those of the Nazis
But Labour has insisted that while the examples are not reproduced word for word, they are covered elsewhere in the new code.
Labour MPs Chuka Umunna, Liz Kendall and Anna Turley are among those who have been critical.
The Jewish Leadership Council and the Board of Deputies of British Jews said in a joint statement that it was "impossible to understand" why Labour had not adopted the IHRA definition in full - as the UK Jewish community, governments and local councils had done.