Staff at Wandsworth and Richmond Councils could strike in opposition to "unnecessarily aggressive" termination letters sent as the shared staffing arrangement press on.

By the end of summer it is envisaged that the two neighbouring councils will share staff, estimated to cut £10m a year from each council's budget.

January 2015: Union raises concerns over job losses following Richmond-Wandsworth merger announcement

December 1: Cuts to front-line council services and council tax increases for residents following Autumn Statement, warns deputy leader​

January 27: "Weaknesses" identified in Wandsworth's children's services leads to staff shake-up ahead of agreement with Richmond

Employees received statutory letters explaining they would be dismissed from their current jobs and re-hired under a different contract.

Frank Minal, from GMB, explained that the most worrying thing for staff in Wandsworth Council was the loss of the performance-related pay scheme.

He said: "The majority of staff in Wandsworth make £1,000 a year in this pay, but for higher management it equates to seven per cent of wages.

"Richmond colleagues have never had this scheme."

Mr Minal said that staff were expecting a second letter with a full proposal by Wednesday and once that had been considered, the union would decide whether to ballot for strike action.

Paul Grafton, GMB regional organiser, said: "GMB will be undertaking a consultative ballot of our members in due course to ascertain what action they may wish to take as a result of the threat.

"GMB is committed to negotiate a better deal for staff than one currently on the table but see the issuing of these statutory notices is nothing short of an unnecessarily aggressive approach that does no more but alienate staff."

Mr Minal said: "Dismissing and re-engaging is a provocative act by any employer.

"It says we cannot negotiate but we reserve the right to dismiss.

"It is an unfortunate situation.

"We hope that Wandsworth can do the right thing and come up with a solution that will be palatable to staff."

Paul Martin, chief executive of Wandsworth Council and Gillian Norton, chief executive of Richmond Council, issued a joint statement.

It read: "As part of our work to create a joint staffing structure across Wandsworth and Richmond Councils, we have been in constructive negotiations with the recognised trade unions since September 2015 in order to agree harmonised terms and conditions for staff from both boroughs.

"Although the councils remain fully committed to further negotiations in order to achieve a Collective Agreement, because of the timetable for the implementation of the shared staffing arrangement, it was necessary to issue the notice as a precaution in order to fulfil the legislative requirement.

"Late last week this position was fully explained to the local trade union representatives at their weekly meeting.

"We are still working towards a collective agreement with the trade unions.

"It is still our aim and hope that this will be achievable.

"We will continue with further talks tomorrow and weekly meetings thereafter."