Last week the council announced it was to transfer almost its entire blue-collar workforce in a £35 million-a-year deal (LGC, 4 October).
The new company is expected to take over in January.
Unison general branch secretary Micky Scales has insisted the council was seeking to offload its responsibilities. He said the externalisation drive, the largest of its kind in Britain, was purely budget-led.
There are also queries about the council's 'golden share', which a spokeswoman said would be 'the minimal'.