Nurses will go on strike for a further two days in February after talks with the government failed last week.
The Royal College of Nursing (RCN) said nurses in England and Wales will walk out for 12 hours on February 6 and 7 unless progress is made on reaching a deal.
In a significant escalation of the industrial action taken so far, 73 NHS trusts will be affected next month, compared with 44 in December and 55 in January.
No action will be taken in Northern Ireland or in Scotland, where strikes have been paused while negotiations with ministers continue.
The RCN’s general secretary and chief executive, Pat Cullen said nurses were striking once again “with a heavy heart”.
“Rather than negotiate, Rishi Sunak has chosen strike action again,” she said.
“We are doing this in a desperate bid to get him and ministers to rescue the NHS. The only credible solution is to address the tens of thousands of unfilled jobs — patient care is suffering like never before.
“My olive branch to government — asking them to meet me halfway and begin negotiations — is still there. They should grab it.”
The announcement of further strike dates heaps further pressure on the government to resolve the dispute and protect patient care.
Nurses are already due to strike on Wednesday and Thursday this week, while the GMB union is expected to announced up to six more strikes by ambulance workers later today.
The RCN is asking for a pay rise of 5% above inflation but Cullen has said she is willing to meet the government “halfway”.
The union says that salaries for experienced nurses today are 20% lower in real terms than in 2010 due to pay rises not keeping pace with inflation.
It says low pay is forcing staff out of the profession and contributing to a record number of vacancies. There were about 133,400 full-time staff vacancies in NHS trusts between July and September last year.
Ministers have repeatedly said that the health unions’ pay claims are unaffordable and have said that any wage rises should be determined by the independent pay review body.
However, the unions have questioned the independence of the pay review body and are refusing to submit any evidence to it for the 2023/24 financial year until the current dispute is resolved.
The Observer reported over the weekend that health secretary Steve Barclay told unions he wanted to persuade the Treasury to offer NHS workers more generous pay offers — a move that may put him at loggerheads with Sunak and Jeremy Hunt.
It comes as MPs are due to vote on the government’s Transport Strikes Bill, which will require employers and trade unions to provide a minimum level of service during industrial action.
It would force NHS staff, firefighters and railway workers to comply with minimum service levels during industrial action.
If they failed to do so, they would potentially face the sack.
The unions have attacked the bill as an attack on the fundamental right to strike and have said they are prepared to robustly oppose the legislation in the courts.