The date for the ambulance workers' strike has now been announced, ITV News correspondent Rebecca Barry has the latest on how the walkout is expected to unfold
Last week the GMB union said its members had voted in favour of strike action, with similar ballots at Unite and Unison also being declared.
The government is bracing itself for a series of strikes by public sector workers in the build up to Christmas, including the biggest ever UK-wide walkout by nurses.
Across England, Wales and Northern Ireland some 100,000 members of the Royal College of Nursing (RCN) will head to picket lines on 15 and 20 December.
And with the date for strike action by ambulance workers now known, here's how you can expect the walkout to take shape.
How the strikes will unfold
When will ambulance workers go on strike?
Thousands of ambulance workers and other NHS staff will strike on December 21, while paramedics, Emergency Care Assistants, call handlers and other staff will also walk out on December 28.
Will the strikes clash with those held by nurses?
No. Industrial action taken on December 21 will happen a day after members of the RCN stage their second walkout.
The December 28 walkout will also not coincide with any strikes announced by the RCN.
Who will be striking and when?
What services will be affected by the strikes?
The strike action by GMB members is set to affect services provided under nine trusts across England and Wales. These include:
South West Ambulance Service
South East Coast Ambulance Service
North West Ambulance Service
South Central Ambulance Service
North East Ambulance Service
East Midlands Ambulance Service
West Midlands Ambulance Service
Welsh Ambulance Service
Yorkshire Ambulance Service.
Industrial action will be taken by those working as paramedics, emergency care assistants, call handlers and other staff.
Unite said more than 1,600 of its members at the West Midlands, North West and North East ambulance service trusts will join the walkout.
And ambulance crews in Unison working for five services in England - London, Yorkshire, the North West, North East and South West - will also strike.
Unison said its strike, involving paramedics, emergency care assistants, ambulance technicians and other 999 crew members, will run from noon to midnight.
Will emergency cover be provided?
After the ballot results were announced, Unison said "emergency cover will be available during any strike" and Unite made clear it will maintain essential emergency cover for patients.
Meanwhile, GMB representatives have said they will meet with individual trusts to discuss requirements for life-and-limb cover.
To help cover the absence of striking public sector workers the government has also placed hundreds of troops on stand-by.
The Cabinet Office said that about 2,000 military personnel, civil servants and other volunteers from across government have been training as part of its contingency planning.
They included up to 600 armed forces personnel and 700 staff from the government’s specialist Surge and Rapid Response Team, as well as from other parts of the Civil Service.
Conservative Party chairman Nadhim Zahawi said it was the "right and responsible thing to do" as ministers sought to minimise the disruption to the public.
ITV News Political Editor Robert Peston on a standoff between unions and the government that is hitting the British public
Why are ambulance workers striking?
Workers across the ambulance services and some NHS trusts have voted to strike over the government’s 4% pay award, which the GMB union described as another "massive real-terms pay cut".
Rachel Harrison, GMB national secretary, said: "After 12 years of Conservative cuts to the service and their pay packets, NHS staff have had enough.
"The last thing they want to do is take strike action but the government has left them with no choice."
Elsewhere, Sharon Graham, Unite general secretary, said: "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."
What has the government said?
Health and Social Care Secretary Steve Barclay said: "NHS workers do an incredible job caring for our loved ones and it is disappointing some will be taking industrial action, ahead of a challenging winter.
"The economic circumstances mean unions’ demands are not affordable - each additional 1% pay rise for all staff on the Agenda for Change contract would cost around £700 million a year.
"We’ve prioritised the NHS with record funding and accepted the independent pay review body’s recommendations to give over one million NHS workers a pay rise of at least £1,400 this year, with those on the lowest salaries receiving an increase of up to 9.3%.
"This is on top of the 3% award last year when wider public sector pay was frozen and on top of the wider government support to help with the cost of living.
"Our priority is to ensure emergency services continue to operate for those who need it and limit disruption, particularly at a time when NHS services are under huge pressure due to the impact of Covid."
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know.