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."