Trade union Unite protested as HBOS shareholders gathered at the NEC in Birmingham to approve the ailing bank's £11.5bn taxpayer bail-out and a takeover by rival Lloyds TSB.
Members of Unite, which fears thousands of job losses as a result of the deal, were armed with mock ballot papers for investors attending the bank's special meeting at the NEC, urging them to consider the interests of staff.
Unite national secretary with responsibility for finance Rob MacGregor said: "We are obviously concerned about redundancies. Assurances on jobs have been few and far between.
"Lloyds TSB have said they want to make £1.5bn in cost savings and from past experience the biggest cost saving they can make is by cutting staff and closing branches."
Approval of the deal will clear the way for a banking giant with around 145,000 staff and 3,000 branches across the UK.
HBOS chairman Dennis Stevenson has warned the bank could face full nationalisation if the deal fails to go through.
Alun Evans, a shareholder in both banks speaking before the meeting, said: "I see no future for HBOS as an independent bank. I would expect there would be a benefit for Lloyds TSB shareholders as well."