Nurses strikes involving twice as many workers will be announced for February if talks with the government do not progress soon, union bosses have warned.
The Royal College of Nursing (RCN) union said that new walkouts would be scheduled should negotiations over pay remain stalled by the end of January.
All eligible members in England would go on strike for the first time, making it the RCN's biggest to date.
Pat Cullen, its general secretary, insisted people backed the nurses in their pay dispute with the government, blaming the prime minister for his "baffling" approach to the negotiations.
The government has insisted nurses have been offered a "fair" pay deal and it has accepted the recommendations of the independent pay review body "in full".
Mark Harper, the transport secretary, was pushed on the issue by Sophy Ridge on Sky News this morning, who pointed to documents showing the government set its budget for pay before hearing from the body, warning them any higher offer could increase inflation.
Mr Harper said it was "important to set out the context" of the economy to the independent body, and that they also received evidence from trade unions before coming to a decision.
He denied the government set the parameters for pay increases, adding: "We've made some assumptions, but we'll look at what the independent pay body says."
But Labour leader Sir Keir Starmer told the government to "do the grown up thing, get in the room and negotiate".
Ms Cullen said ministers risked forcing nurses to quit the health service en masse.
"The nurse shortage costs lives - Sunak cannot put a price on a safe NHS," she said.
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Potential strike date
Members are likely to take action on 6 February, the RCN said, to coincide with the 10th anniversary of an inquiry that looked into how nurse shortages affected patient mortality.
The Robert Francis inquiry, which was focused on Mid Staffordshire NHS Trust, uncovered the neglect of hundreds of patients at Stafford Hospital between 2005 and 2009
Some elderly people were left lying in their own urine, unable to eat, drink or take essential medication.
Mr Francis has warned that the NHS crisis is "Mid Staffs playing out on a national level, if not worse".
The Department for Health and Social Care showed no sign of a change in approach in a statement on Saturday night, which said more than one million NHS workers had received a minimum £1,400 pay rise this year.
The spokesman added: "This is on top of a 3% pay increase last year when public sector pay was frozen and wider government support with the cost of living."
No sign of end to wave of action
The latest threat from the RCN union comes before walkouts on Wednesday and Thursday, when nursing staff from more than 70 NHS trusts are set to strike.
This includes 55 trusts in England that were not involved in the first wave of action in December.
If RCN members strike in February, they will join nurses in Wales who are already expected to take action.
There are not any planned walkouts in Northern Ireland, where there is no executive in place at Stormont, or Scotland, where negotiations with the Holyrood government are ongoing.
Hundreds of thousands of workers across many sectors of the economy, from rail and mail to civil servants and bus drivers, have gone on strike this winter in disputes over pay and conditions as unions fight to keep salaries in line with soaring inflation.
If you are an NHS worker and would like to share your experiences with us anonymously, please email NHSstories@sky.uk