Council and school support staff are to strike on July 10 after voting in favour of industrial action over pay.
Unison said its members in England, Wales and Northern Ireland will walk out for 24 hours, with other unions set to announce a similar move in the coming week.
Unison announced that its local government members backed action by 58 per cent in protest at a pay offer worth one per cent for most workers.
General secretary Dave Prentis said: “We have a clear majority for strike action so a one-day strike will go ahead on July 10. We expect to be joined in that action by other unions in local government and will be campaigning amongst our members for maximum support on that day.
“Many of our members are low-paid women earning barely above the minimum wage, who care for our children, our elderly and our vulnerable and they deserve better treatment than they have had at the hands of this government. The employers must get back into talks immediately to avoid a damaging dispute.”
Unison said local government workers have been “condemned” to three consecutive years of pay freezes, followed by below-inflation rises in 2013 and 2014, leaving their pay reduced by almost 20 per cent since the coalition came to power.