Job-seekers, people collecting benefits and those applying for passports could all face problems after tens of thousands of civil servants voted to strike in a row over pay and pensions.
Some 100,000 members of the Public and Commercial Services (PCS) union overwhelmingly backed taking industrial action.
The union warned that unless it received “substantial proposals” from the government, it would announce a programme of “sustained industrial action” next Friday.
The ballot result came a day after nurses voted to strike and shortly before Aslef announced train drivers at 12 operators are to strike on November 26 in their long-running dispute over pay.
The PCS said 126 employer areas could be hit by major industrial action, including the Home Office, which includes Border Force officials and passport workers, the Department for Transport, including driving examiners, and the Department for Work and Pensions, including staff in job centres and those processing benefits.
The PCS said the average ‘yes’ vote for action across the areas balloted - 86.2 per cent - was the highest percentage vote in the union’s history.
As well as pay and pensions, the dispute covers jobs and redundancy terms.
Under Boris Johnson, the government set a target of 91,000 job cuts in the civil service. But Rishi Sunak, when he became prime minister, scrapped the target and ordered departments to find efficiency savings instead as part of a drive to find £50bn savings.
Employee numbers had been expanded to help deliver Brexit and to fight Covid.
The civil service grew by the equivalent of more than 4,000 full-time jobs in the first three months of this year.
There were 479,040 employees as of March, up from 474,900 in December, according to the Office for National Statistics (ONS). It was the highest number of full-time equivalent roles since 2010.
The prime minister’s spokesman said reductions would still be needed, but declined to put a specific number on them.
Union general secretary Mark Serwotka said: “The government must look at the huge vote for strike action across swathes of the civil service and realise it can no longer treat its workers with contempt.
“Our members have spoken and if the government fails to listen to them, we’ll have no option than to launch a prolonged programme of industrial action reaching into every corner of public life.
“Civil servants have willingly and diligently played a vital role in keeping the country running during the pandemic but enough is enough.
“The stress of working in the civil service, under the pressure of the cost-of-living crisis, job cuts and office closures means they’ve reached the end of their tethers.
“We are calling on the government to respond positively to our members’ demands. They have to give our members a 10 per cent pay rise, job security, pensions justice and protected redundancy terms.”
A government spokesperson said: “We regret this decision and remain in regular discussion with unions and staff.
“As the public would expect, we have plans in place to keep essential services running and minimise any potential disruption if strikes do go ahead.
“The public-sector pay awards are a careful balance between delivering value for money for the taxpayer and recognising the importance of public-sector workers.”