More than 124,000 civil servants in 186 government departments are to be re-balloted for strike action that could last until December, it has been announced.
The Public and Commercial Services (PCS) union said the new ballot will run from March 20 to May 9 and could see the strike mandate renewed for another six months.
Unions involved in industrial action have to hold a fresh ballot every six months.
PCS members including civil servants in government departments, Border Force, the DVLA and the British Museum are among those who have been taking industrial action for months in a dispute over pay, pensions and jobs.
Workers at the Land Registry and DVLA will be on strike next week, while 100,000 civil servants will walk out on Budget day, March 15.
PCS general secretary Mark Serwotka said: “We’re sending a very clear signal to ministers that we’re not backing down in the pursuit of a fair deal for our members.
“The pressure is building on ministers. They’re being forced to talk to us, to listen to our concerns, and they now know we’re looking at escalating our strike action beyond May, unless they make concessions.
“Our members deserve a fair pay rise and we will not stop our campaign until ministers put money on the table.”