Members of Northern Ireland's largest health workers' union have served notice to employers of industrial action to being next week.
The action by Unison members, which represents 25,000 nurses, ambulance staff, support staff and social care workers, comes amid a dispute over pay and staffing levels.
On November 11, 23% of Unison members took part in a ballot on industrial action, with 92% voting in favour of striking.
The ballot came a week after members of the Royal College of Nursing (RCN) in Northern Ireland voted to strike, the first time in the RCN's 103-year-history such action has been taken in the UK.
RCN members will begin action short of a strike on December 3, with a full walkout taking place on December 18.
Unison has announced phase one of their industrial action will run from November 25 to December 18, while phase two will run from December 18 to March 2020.
This means both the Unison and RCN industrial action on December 18 will overlap - potentially causing chaos across Northern Ireland's healthcare system.
The first phase will see health workers across Northern Ireland's five health trusts start industrial action short of a strike.
This action will include:
Specific groups of health workers will take part in different stages of the industrial action.
From the first week, this will include workers in sterile services across major hospitals and hospital and social services transport staff across the Belfast and Northern trusts.
Support services employees, such as porters and catering staff, based at the Ulster Hospital and Lagan Valley Hospital will also take part, as well as portering services staff at Craigavon Area Hospital.
Strike action by these groups of workers will take place over different time periods and at different locations, with employers receiving seven days notice prior to each week of strike action.
Unison regional secretary Patricia McKeown said the decision to strike was not taken lightly.
"They are determined to fight for justice on both pay and staffing levels. They are determined to break the cycle of hundreds of millions of pounds haemorrhaging out of the health budget and into the hands of private agencies," she said.
"They are determined to see our NHS workforce stabilised and allowed to get on with the serious business of delivering health and social care to the people of Northern Ireland."
Ms McKeown said Unison is aware the Northern Ireland public's support for the campaign and is challenging healthcare bosses to "match the courage and determination of the workforce to save the health service from further crisis".
"The workers are standing up for justice. It is time they did so too," she added.
A Department of Health spokesperson said: "The Department remains focused on finding a way forward and remains fully committed to ongoing dialogue."