Thousands of council workers were said to be in shock today after receiving letters warning that they could lose their jobs under plans to slash spending.
The GMB said it was organising a mass meeting of its members in Birmingham City Council to decide how to respond to the "crisis".
Regional officer Joe Morgan said: "The workers have been told if they don't accept new contracts they will be dismissed and re-engaged on worse conditions.
"The council's chief executive is acting like a school bully by saying that workers have to accept this or they will be sacked without compensation. Our members are in shock and are up in arms."
Mr Morgan said unions representing workers at the council would co-operate in their response to the letters.
The council confirmed it had issued warning notices to 25,000 staff but said no figure for any job cuts had been decided.
Chief executive Stephen Hughes said: "It is estimated the council will need to reduce its net expenditure by £330 million over the next three to four years, which equates to around a third of our overall net spend.
"The magnitude of this financial pressure is immense. The council needs to radically review its overheads and expenditure and, as part of this, there is a need to broaden the existing review of employee allowances and terms and conditions of employment which began earlier this year.
"We also have a duty to ensure that any payments that we make to employees are fair and meet the legal requirements of equal pay legislation."Reuse content