More than a million public sector workers will vote on whether to strike next week in an ongoing row over pensions.
It could spell misery for schools and hospitals as nurses, teaching assistants, dinner ladies and hospital cleaners number among those debating whether to strike.
Social workers and probation officers will also vote on strike action.
It will be the biggest-ever union industrial action ballot in Britain, and is the first time that Unison – Britain's biggest public sector trade union – has ballotted its entire membership on strike action.
If the majority vote in favour of action, Unison will ask members to strike on November 30. The results of the ballot are expected by November 3.
Unison's general secretary Dave Prentis said the union was fighting against "attacks" by the government.
Workers are angry at the prospect of increased contributions, a later retirement age and reduced pensions.
However, Prentis promised that essential public services would be protected on strike days.
He said: "We are doing everything possible to get a high turnout and we are confident of a big 'yes' vote.
"This is a fight not just about whether it is right to increase contributions, but it's a fight for the survival of public service pension schemes."