Over 100,000 civil servants are to strike on budget day in an escalation of a dispute over pay, pensions and job security.
The PCS union has announced a new strike date of 15 March, when Chancellor Jeremy Hunt is due to unveil his spring budget.
It follows a strike last week that saw hundreds of thousands of members in 123 government departments walk out across England, Scotland and Wales.
The union warned that next month’s strike could be joined by a further 33,000 members working for 10 more employers, including HMRC, whose ballot results are due on 28 February.
PCS general secretary Mark Serwotka said: “Rishi Sunak doesn’t seem to understand that the more he ignores our members’ demands for a pay rise to get them through the cost-of-living crisis, the more angry and more determined he makes them.
“PCS members are suffering a completely unacceptable decline in their pay. By April, one third of HMRC staff, for example, will be earning just the minimum wage. 40,000 civil servants have used a foodbank. It’s an appalling way for the government to treat its own workforce.”
Mr Serwotka said the prime minister “can end this dispute tomorrow if he puts more money on the table”.
He warned: “If he refuses to do that, more action is inevitable.”
The PCS union is calling for a 10% pay rise, protections to pensions and protections from job cuts.
The government has said the demands would cost £2.4 billion which is unaffordable.
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Mark Serwotka says that industrial action is likely to grow unless demands are addressed by government.
The dispute is becoming increasingly bitter with Mr Serwotka calling talks last month to prevent the action a “complete farce” and warning future strikes “will be even bigger” if ministers do not act.
The strikes have impacted several key government departments including Border Force, National Highways, the Department for Work and Pensions and the DVLA.
The new members being balloted include those working for HMRC, the Welsh government, the Care Quality Commission and Companies House.
Civil servants are among the thousands of public sector workers striking over pay and conditions amid soaring inflation and a decline in living standards.
Nurses continued with their industrial action today after walking out on Monday alongside paramedics and call handlers in what was the largest strike in NHS history.
Environment Agency workers will walkout tomorrow while teachers and university staff will continue with strikes next week.
Union leaders have implored the government to act to prevent further strike action, but ministers in England have indicated that they will not budge on one of the main points of contention – pay for 2022/23.