Up to 750,000 public sector workers will join a mass walkout later this month after members of a third union backed industrial action.
The PCS said its 290,000 members had to defend themselves against "attacks" on their pensions by the government.
The civil servants will strike on 30 June - the same days as hundreds of thousands of teachers and lecturers.
Book July 1st off and you can get a 4 day weekend!!