The prospect of a huge strike on July 10 has come closer after members of a leading union backed industrial action over pay.
The GMB said its members in councils and schools in Wales, England and Northern Ireland supported strikes by 3-1 in protest at a 1% pay offer.
The Government is now facing a walkout by more than a million public sector workers next month, including council staff, teachers and civil servants.
GMB national officer Brian Strutton said "Our members have spoken loud and clear and said they want to go on strike.
"We have tried sensible discussions, we've sought to negotiate reasonably, we've said we are willing to accept Acas arbitration rather than go on strike - but to everything we've tried, the employers have said no. So we have no choice.
"GMB members serving school meals, cleaning streets, emptying bins, looking after the elderly, helping children in classrooms and in all the other vital roles serving our communities are fed-up with being ignored and undervalued.
"Their pay has gone up only 1% since 2010 and in October even the national minimum wage will overtake local authority pay scales.
"Their case is reasonable, the employers won't listen and don't care. No wonder they have turned to strike action as the only way of making their voices heard.
"With other unions involved too, July 10 looks like being the second biggest dispute ever, with up to two million workers on strike."
The GMB said there were 26,281 votes in favour of strike action and 9,799 against. Turnout was 23%.
A Local Government Association spokesman said: "It is disappointing that GMB will be proceeding with strike action when the turnout was so low. Local government staff have worked wonders while councils have been tackling the biggest funding cuts in living memory and we have no doubt that many will still be at work on the day of strike action.
"The pay offer we have made would increase the pay of most employees by 1% while the lowest paid would receive an increase of more than 4%. This is the fairest possible deal for our employees given the limits of what we can afford.
"This strike will not change the pay offer we have made, but it will mean those who take part lose a day's pay."