The frontrunners in Labour's leadership contest have joined forces to call for a moratorium on an internal reorganisation that could see some party staff sacked within days.
Jess Phillips, Keir Starmer, Lisa Nandy and Rebecca Long-Bailey, who are all either confirmed or likely to stand for leader, and Angela Rayner who is standing for the deputy leadership, appealed to party chiefs to put a halt to any snap reorganisation.
Sky News has seen a letter from the Unite and GMB to the leadership and deputy leadership contenders urging them to put their name to the statement urging a halt to any "purge" of staff members before a new leader is chosen.
This will add heft to the growing campaign to stop rapid changes after Labour's disastrous election campaign. Some Labour staff members received emails that week from the human resources department saying they were at risk of redundancies.
Jeremy Corbyn's chief of staff Karie Murphy and the party's general secretary Jennie Formby are reportedly drafting a major overhaul of party structures before he steps down in the spring.
The plans could include reducing the analytics team and election teams at Labour headquarters and replacing regional staff with community organisers.
The decision by Unite and GMB to send the letter is significant, as both unions could have a big influence on the contest.
Leadership candidates are being asked to sign up by lunchtime on Tuesday.
The letter says: "We feel that any decision on the organisational structure and direction of the Labour Party should be taken after the leadership and deputy leadership contest.
"All staff appreciate the support that you and other members of parliament have shown over the last weeks and months and we would appreciate if you could support the below statement. Ideally if you could let myself and Paul know by 12 noon tomorrow we would be most grateful."
The statement says: "The 2019 General Election was a disastrous result for the country and our party. There are vital lessons we must learn politically and organisationally if we are to deliver Labour to power at the next election. There are no easy answers, no one individual or section of our movement holds the key.
"There are presently elections for a new leader and deputy leader. Throughout the contest we will debate the future of our Party, what we got right and where we need to change.
"That is an important part of Labour's democracy - making sure all voices are heard. Our newly elected leaders, must set out their vision for the future and once elected work across our movement with our trade unions, affiliates, National Executive, activists, councillors, members and voters to plan that path back to government.
"As candidates in the leadership and deputy leadership campaigns we firmly believe that a thorough review should be the duty and responsibility of the next leadership team when a full and frank debate has taken place.
"It would be a mistake for the party to undertake any steps towards reorganisation of the party until a new leader and deputy leader are in place."
Ms Nandy said: "Decisions on the future structure of the Labour Party should not be made in haste. We need to listen and learn the lessons from this election defeat and rebuild from there. It will take change from the top to the bottom of the Labour Party but we must do it together and in the right way."
Mrs Phillips said: "This statement from Unite and GMB has my full support. Staff deserve better and the new leadership team will want to make a fresh start. I am particularly concerned about rumoured changes to our regional offices. They're the backbone to successful campaigns. Learning lessons from our defeat means listening to our front line staff, not hurriedly pushing them out the door."
Mrs Rayner said: "Any big reorganisation ahead of a new leadership team coming forward would be very regrettable at this moment in time and questionable as to why we'd want to do that."
A spokesperson for Ms Long-Bailey, said: "If these reports are true then no decisions must be made in haste and it would be misguided for restructuring to take place before the installation of the next leader of the party, and any changes must be subject to full consultation with trade unions."
A spokesperson for Mr Starmer's campaign said: "Keir wholeheartedly supports this statement. Hard working staff need immediate reassurance, not a rushed reorganisation. It's important any structural changes to the Labour Party are undertaken by the new leadership team following a full consultation with staff and trade unions."
Labour sources say organisational review is common after a general election but that nothing has been decided or that anyone is being "fired". Any changes would be subject to consultation with the relevant trade unions.