Two trade unions, representing members of staff in Jeremy Corbyn’s office, have written to the Labour Party raising concerns about the team’s treatment following a major shake-up of internal structures.

Unite the Union and Communication Workers Union (CWU), have complained to the party's general secretary, Jennie Formby, after 37 members of Corbyn’s staff were called to “informal meetings” about their roles in his office.

Correspondence, seen by ITV News, says there was no prior consultation with the unions about the internal review and no warning was provided that members of staff would be called for interviews immediately.

The unions, which sit on Labour's all powerful National Executive Committee (NEC), have advised their members to decline the interview invitations.

In one email, members of staff in Mr Corbyn’s office are advised that if they are forced to go to the meetings, they should make a note that they are attending “under duress”.

An email said: "If the party insist on going ahead and choose to ignore the correct meaningful consultation process, (which any reasonable employer with decent trade union industrial relations would follow) we would advise our members to have minuted they are attending their meeting under duress without the requested union representation to protect their legal position going forward."

ITV News has also seen correspondence between members of the NEC who have voiced discontent about the way in which the restructuring has been handled by the Labour leader’s office.

One well connected source told ITV News the NEC are set to demand explanations for why this review has taken place and that Corbyn was now considering asking for a “slowdown” of the restructuring.

Members of staff in Mr Corbyn’s office had raised concerns directly with management that some interviews had taken place with trade union representation being offered, as revealed by ITV’s Political Editor Robert Peston.

In one email a senior member of staff said there were worries about job losses and noted a commitment that trade unions would be involved in the process had “so far not happened.”

However, a Labour source hit back at the unions for intervening.

The source said: “Staff in the Leader’s office backed the review and agreed it should go ahead, while also proposing some changes.

“Unions should really speak to their members in the workplace before writing to the general secretary next time.”

The interviews - which have been described as “entirely voluntary” - are taking place from October 14 to October 18 and are led by the former head of the civil service Sir Bob Kerslake, a long-time friend of John McDonnell.

Sir Bob Kerslake is a long-time friend of Labour's shadow chancellor John McDonnell. Credit: PA

Mr Kerslake worked with the shadow chancellor at the Greater London Council in the 1980s and has been working with Mr Corbyn and Mr McDonnell on how to reform the Labour Party’s internal structures.

The restructuring of Mr Corbyn’s office started last week and the Labour leader’s chief of staff Karie Murphy and his political secretary Amy Jackson have been moved to Labour Party headquarters.

The rejig was described as preparation for a potential general election.

A Labour Party spokesperson said: “We don't comment on staffing matters.”

Unite and CWU have both been contacted for comment.

An earlier version of this report stated the TSSA union had also made a complaint. A complaint had been made by someone linked to the TSSA but this was not on behalf of the union.