The shadow secretary of state for Northern Ireland Vernon Coaker has joined seven other members of the shadow cabinet and resigned.
The resignations follow the sacking of shadow foreign secretary Hilary Benn overnight.
He has released a statement saying he believes it is "time for the party to unite behind a new leader" and serve as an "effective opposition".
He adds: "I have sought to make it my priority to provide reassurance to the people and political parties of Northern Ireland that Labour remains committed to the principle of consent, as expressed through the Good Friday Agreement and subsequent agreements.
"I know my successor in this role continues this vital work."
Seema Malhotra, shadow chief secretary to the Treasury, has resigned from the shadow cabinet, sources said.
The MP is one of seven Labour cabinet members to have quit on Sunday, but ITV News Deputy Political Editor Chris Ship has said this resignation is "different" as she is closer to Mr Corbyn that her colleagues.
Shadow home secretary Andy Burnham has said he will not be taking part in a "coup" against Labour leader Jeremy Corbyn.
"At an uncertain time like this for our country, I cannot see how it makes sense for the Opposition to plunge itself into a civil war," he said.
Labour MP Lucy Powell has resigned as shadow education secretary, saying that Jeremy Corbyn's position as leader of the party is "untenable".
In a letter to the Labour Party leader, she said: "It is increasingly clear that your position is untenable and that you are unable to command the support of the Shadow Cabinet, the Parliamentary Labour Party and, most importantly, the country.
Given the big challenges faced by our country and our Party over the coming months, and the possibility of an imminent general election, I do not have the confidence that you can bring the Party together, lead us to a General Election and be an effective Opposition.
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Ann Coffey has added to the growing list of Labour MPs who have said that Jeremy Corbyn must go in the wake of the EU referendum, saying the public have "no confidence" in him.
She also criticised his campaigning over the referendum, saying that it was "lacklustre, it was unenthusiastic" and that he came across as not caring about the result.
Ann Coffey has seconded a vote of no confidence in Mr Corbyn that Labour MPMargaret Hodge proposed.
Labour MPs are being asked to support shadow chancellor John McDonnell in a potential leadership takeover, ITV News understands.
A source within the party said shadow chief secretary to the Treasury, Seema Malhotra, has been ringing around to try to canvas support.
Reports suggest she may be among the wave of resignations by shadow cabinet members expected today.
Jeremy Corbyn said has no intention of stepping down as leader of the Labour party, a spokesman said today.
Jeremy Corbyn is the democratically elected leader of the Labour Party and will remain so.
The Labour leader remained defiant even as he faces a wave of resignations from his shadow cabinet.
Party sources told ITV News that around ten members of the front bench are set to quit today.
Union members on Labour's National Executive are set to call for unity and confirm their support Jeremy Corbyn's leadership, sources said.
A statement is expected later amid union anger at the moves by members of the shadow cabinet against the Labour leader.
Jennie Formby, one of Unite's representatives on the National Executive Committee (NEC) said it was "nonsense " to blame Mr Corbyn for the referendum result and said Labour MPs should show unity.
John McDonnell insisted he will "never" stand for the Labour leadership as he said the party should stand by current head Jeremy Corbyn.
Labour MPs were being canvassed over their support for the shadow chancellor in a potential leadership takeover, ITV News understands.
However Mr McDonnell said he had no desire to take over the top job in an interview with the BBC's Sunday Politics programme, adding: "Jeremy's not going anywhere".
I will never stand for the leadership of the Labour Party. If Jeremy has to stand for another leadership election, I will chair his campaign and I think the Labour Party members will elect him again.