BBC: Up to 750,000 public sector workers will hold a co-ordinated strike later this month after members of a third major union backed industrial action.
The PCS said its 290,000 members had to defend themselves against "attacks" on their pensions by the government.
But ministers called it "irresponsible" and said the 32.4% turnout showed the strike had "extremely limited support".
The civil servants will walk out on 30 June - the same days as hundreds of thousands of teachers and lecturers.
The National Union of Teachers and the Association of Teachers and Lecturers have announced a nationwide walkout, affecting thousands of schools in England and Wales.
Alongside action from PCS members - who include court staff, immigration officers and air traffic controllers - it will be the biggest outbreak of industrial unrest in the public sector for many years.
Labour leader Ed Miliband wrote on Twitter: "Strikes are a sign of failure on both sides. Government needs to get round table not ramp up rhetoric." (+video) » | Wednesday, June 15, 2011
