Up to 100,000 civil servants could join 600,000 local government workers on strike in July, as 40,000 more council workers in Unite pledge to strike too.
One of the biggest outbreaks of industrial unrest for years will see tens of thousands of job centre workers, coastguards, driving examiners and other Government employees join a strike next month by council employees.
More than half a million local authority workers in England, Wales and Northern Ireland are staging a two-day walkout on July 16 and 17 after rejecting a 2.45% pay offer.
Members of Unite, the country's biggest union, representing 40,000 local government workers, voted by three to one to join the strike which is threatening to disrupt refuse collections, schools and social services.
Mark Serwotka, leader of the Public and Commercial Services union, revealed up to 100,000 civil servants at a number of Government departments could also take industrial action on one or both of the same days because of long-running disputes over pay.
The Department for Work and Pensions, Transport Department and Home Office are some of the Government departments likely to be involved.
The union is in dispute with around 14 departments over pay and jobs and have already held a number of strikes.
The PCS will ballot its entire membership later this year for a fresh round of industrial action but it already has mandates to call strikes in a number of departments.