The three civil service unions are refusing to rule out strike action over Chancellor Gordon Brown's decision to cut 40,000 Whitehall jobs.
Brown: "This is the right decision"
The Public and Commercial Services Union, First Division Association and Prospect are holding urgent meetings to discuss the issue.
Mr Brown told BBC News making "big redundancies" would show he had the strength to make "tough decisions".
But angry union members have branded his Budget announcement "unacceptable".
Prospect and the First Division Association (FDA) told BBC News Online they could not yet comment on the likelihood of strike action.
Public and Commercial Services Union (PCS) general secretary Mark Serwotka said the unions had expressed their anger and dismay at a meeting with senior cabinet officials on Thursday.
The unions also expressed dismay that compulsory redundancies had not been ruled out, and called for an urgent meeting with the Cabinet Office Minister Douglas.
The PCS described Budget day as "a day of the long knives for public servants across the UK".
Mr Serwotka said: "For thousands of hard-working staff to hear they are losing their jobs totally out of the blue without consultation is unacceptable."
"Being told by the chancellor on TV that you have lost your job is as bad as being sacked by text."
The Department of Work and Pensions and the Education Department will bear the brunt of the job cuts but all departments will have to cut their administrative costs by at least 5% by 2008.
Mr Brown also unveiled plans to relocate 20,000 civil servants from London to the regions, saving an estimated £2bn over 15 years.
Mr Brown says the cuts and other measures will save £20bn, allowing him to move funding into health, education and policing.
But Mr Serwotka said: "If the government is serious about tackling tax evasion and the growing problem of smuggling and about delivering full employment, cutting thousands of
jobs is hardly going to help."
The PCS is already in a pay dispute with several government departments.
Last month, it said 80-90% of its members had taken part in a walk-out from job centres and benefits offices, disrupting services.
The latest in a series of strikes is planned for April.
Paul Noon, general secretary of Prospect, which represents 40,000 civil servants, also said his members had been battered by one blow after another with no consultation or prior warning.
"It is a myth all public servants are bureaucrats working in backroom
"Government priorities on the environment, transport, defence and health can only be delivered by professionals.
"They are the true front line, and they are
all public servants.
"They must not fall victim to swingeing attacks on waste and bureaucracy. They need more resources, not less."
The FDA, which represents senior public servants, also expressed its "considerable concern".
Mr Baume said the union would resist all compulsory redundancies.
"We see no justification whatsoever for any compulsory redundancies.
"No one should underestimate the implications of these cuts for individual civil servants at all grades and their families."