Thousands of ambulance workers and other members of NHS staff across most of England and Wales have announced they will strike on 21 December in a dispute over pay.
The strike was announced by the three unions that represent the majority of ambulance unions: the GMB, Unison and Unite unions.
It will be a co-ordinated walkout by paramedics and control room staff from all three unions but it will affect non-life threatening calls only.
Unison, which represents twice as many staff as the other two combined, only has a strike mandate for half of England's 10 regional services. The East of England is completely unaffected.
All of the unions have asked for pay rises that are above average but the governments of England and Wales have given NHS staff an average rise of 4.75% - a minimum of £1,400.
Royal College of Nursing members are also preparing to go on strike on 15 and 20 December in parts of England, Wales and Northern Ireland.
Sara Gorton, head of health at Unison, said: "The government will only have itself to blame if there are strikes in the NHS before Christmas.
"Ambulance staff and their health colleagues don't want to inconvenience anyone. But ministers are refusing to do the one thing that could prevent disruption - that's start genuine talks about pay.
"Wages are too low to stop health workers quitting the NHS. As more and more hand in their notice, there are fewer staff left to care for patients. The public knows that's the reason behind lengthy waits."
Sharon Graham of Unite added: "Make no mistake, we are now in the fight of our lives for the very NHS itself. These strikes are a stark warning – our members are taking a stand to save our NHS from this government.
"Patients’ lives are already at risk but this government is sitting on the sidelines, dodging its responsibility to sort out the crisis that it has created.
"Ministers can’t keep hiding behind the pay review body. They know full well it does not address the desperate need to get huge numbers of NHS workers off the breadline.
"Fail to act now to avert these strikes and the blame will rest firmly at the government’s door."