Union representatives said there was a 50/50 chance of further industrial action after the council said it would transfer 70% of IT staff to Capgemini under Tupe rules.
Members of the IT department walked out for 10 weeks in protest over the council's outsourcing process last autumn. There was further anger earlier this month when the council rejected staff calls to be seconded, rather than transferred, to Capgemini. It had earlier rejected a bid by council IT staff to remain in-house.
Unison regional organiser Jeff Baker said the council had approved the Capgemini deal and employment transfer "on the nod" without considering alternatives. He said this was causing resentment among IT staff as the deal goes ahead.
"I do not think there is a shred of goodwill [among staff]. After the efforts they have made, people now think, 'what do we owe the authority?'"
A council spokesman said the IT department's proposals were considered but the plan to transfer IT staff to the supplier was preferred because it offered better value and faster return on investment. In addition, secondment created greater legal risks.
Alex Blue, director at outsourcing consultancy Orbys, said there were examples of successful secondment, or co-sourcing, deals. Although the initial cost could be greater, these arrangements could offer greater value in terms of knowledge transfer, he said.
Nigel Roxburgh, director at the National Outsourcing Association, warned of the risk of failure in projects where staff did not have a positive view of the deal.
"The worst that can happen is that you end up with a team that is so dispirited that they fight [the contractor] tooth and nail. Everything that the supplier puts up may be attacked by the client account team."
Capgemini said it could not comment during negotiations.