Mark Serwotka, the union's general secretary, said time was "running out for government, who have failed to give guarantees over compulsory redundancies and deteriorating services, as they plough on regardless in cutting civil service jobs."
He added: "Unless the government move to address these problems seriously in the next few weeks, then the possibility of a second national civil service-wide strike will become a reality."
He told journalists on the eve of the TUC's annual conference that his members - a third of whom earn less than £14,000 a year - would not accept what amounted to pay cuts over the next three years. He said that with the retail price index running at 3.3%, they could accept pay rises of 1.9%.
The union had set a timetable until the end of next month to consult its activists but if the government did not change its policy there would be a consultative ballot on a national strike, which could come in waves to disrupt individual departments.
"My members can't stand by when the government is spending £2.2bn a year on consultants, and employing consultants in the Revenue and Customs on salaries at 10 times the rate of civil servants," he said.
Whitehall has already had a series of one-day strikes and work-to-rule in departments varying from benefit office staff to driving instructors. He said his driving instructor members were angry that they were being asked to do "a lot of bureaucratic back office work" in addition to their frontline responsibility for taking driving tests and road safety.
The union has already linked up with other public sector unions to campaign against cuts and privatisation and hopes to persuade the TUC conference this week to vote for a national campaign of protests and demonstrations.
Mr Serwotka yesterday became the first union general secretary to praise John McDonnell, the leftwing Labour MP who wants to challenge Mr Brown for the Labour leadership. He is standing on an anti-privatisation programme. He said Mr McDonnell was more in touch with frontline civil servants than Mr Brown.
But his union members, who are not affiliated to Labour, will not have a say in the leadership election.
