Union chiefs fear tens of thousands of NHS staff will quit rather than be forced to have mandatory Covid jabs.
An estimated 90,000 health workers are still unvaccinated.
But from April frontline NHS staff in England will be moved to other roles if they are not jabbed.
The TUC fears the rule will spark a mass exodus of staff from a service which already has 93,000 vacancies.
Frances O’Grady, the TUC’s general secretary, said: “We are in the middle of an NHS staffing crisis, born not only from Covid absences but also long-term problems that need long-term solutions. Now is not the right time to introduce more bureaucracy.”
Calling for a delay to the jab plan, she added: “The Government’s own impact assessment of its policy concluded that as many as 73,000 staff may leave rather than get jabbed.

“Women, people from ethnic minorities and younger workers are among those most likely to quit.”
Her warning came as a London hospital said yesterday it could lose 1,000 staff members.
Dr Clive Kay, head of King’s College Hospital in South London, said he was “worried” as around 10% of approximately 14,000 workers at the hospital are yet to receive a first dose.
He said: “The law is now such that individuals who are not vaccinated if they can’t be redeployed, will not be able to work in hospitals if they deal with patients.”
Dr Kay said more than 1,000 members of staff could be lost in an “extreme” scenario unless vaccine uptake improves.
He added: “We’re having conversations with staff, their line managers are having conversations, we have a helpline where colleagues seek clarification and help.”

Last week Steve James, a consultant anaesthetist on the hospital’s ICU ward, told Health Secretary Sajid Javid during a visit that he was “not happy” about the new rules. He said: “I have not had a vaccination. I do not want to have a vaccination.”
The latest NHS England data shows 94% of NHS trust staff have had at least one dose of a Covid-19 vaccine and 74% have had a booster dose.
Mr Javid said yesterday nine out of 10 Covid patients being treated in intensive care have not had boosters.
He believes compulsory jabs for NHS staff will cut the number of patients contracting Covid in hospital.
Education Secretary Nadhim Zahawi yesterday backed the requirement for NHS staff to be vaccinated.
He said: “I think when you work with the most vulnerable people – and those going into hospital are very vulnerable, as are those in our care homes – you have a duty of care.” But some NHS medics have started wearing purple ribbons to signal their opposition to being forced to have the vaccine.
A Twitter account called NHS100k, which has more than 18,000 followers, has posted pictures of nurses, radiologists and scientists all wearing purple bows. It says it is: “Uniting more than 100K NHS staff who stand in favour of freedom of choice, bodily autonomy and informed consent.”
Britain reported 141,472 new cases of COVID-19 on Sunday, down from 146,390 cases on Saturday, while the number of new deaths reported fell to 97 from 313.
But a health chief in the area which has seen a soaring infection rate has warned the NHS could be swamped.
Copeland in West Cumbria recorded the country’s highest number of new infections in the seven days to January 1, with 3,076 cases per 100,000, an increase of 130% on the previous week.
Cumbria County Council director of public health Colin Cox said: “The number of cases now is so high that even if a small percentage is hospitalised, there is still a real risk to services.
The number of people who might end up in hospital gives me cause for concern. The staffing level is absolutely critical not just in Cumbria, but right across the NHS.”
Some patients waiting to be admitted to over-stretched hospitals are watching Netflix in ambulances.

Tracy Nicholls, chief executive of the College of Paramedics, said there are delays of up to seven hours at some hospitals and doctors were offering minor treatment and diagnostics like blood tests in car park.
Nineteen ambulances were pictured queueing outside Torbay Hospital and Devon last week.
“Paramedics are spending time apologising to everyone for their waits and distress,” she said.
“If you’ve got a tricky relationship with the patient, you could be sitting with them for several hours in a metal box and tensions can build.
“I’ve heard some crews have streamed Netflix on to their trust iPads and strapped [them] to the stretcher so patients who are able can watch shows while they wait.”