Hundreds of thousands of NHS workers are due to start voting on whether to accept the Government's controversial pension reforms, with a "no" vote set to spark fresh strikes.
Unison said its 450,000 health service members in England, Wales and Northern Ireland, including nurses, therapists, paramedics, cooks, cleaners and porters, will be balloted in the next few weeks.
The move follows votes over Easter by the two biggest teachers' unions for further industrial action, including strikes, over pensions, pay and job losses.
Delegates at the annual conferences of the National Union of Teachers and the NASUWT both backed industrial action, following a strike last November by more than one and a half million public sector workers, and by thousands of teachers and lecturers in London last month.
There is speculation that another strike by public sector workers could be held on May 10 as part of continuing opposition to the pension changes.
Christina McAnea, Unison's head of health, said: "The union will be giving full and open information on what it will mean for individual members' pensions, so they are in the best position to make an informed decision.
"We are still disappointed that the proposals don't meet all our aspirations for health workers, particularly around the retirement age. But the ballot papers will also recognise that rejecting the offer would require members to take further industrial action.
"We have given a commitment from day one that it is for our members to decide and we are keeping to that commitment. This is a massive consultation exercise far bigger than any other in the trade union movement."
The result will be known at the end of April.