A five-week consultation on mandatory jabs has been launched following concerns about whether enough carers have been vaccinated to stop the virus spreading to residents.
But the move has provoked criticism from trade union Unison which said mandatory vaccinations could "backfire" and lead to a staffing shortage.
In Buckinghamshire, 3,632 out of 4,873 eligible staff, including agency workers, at older adult care homes had received a first dose by April 11, according to latest NHS figures – meaning 25% have not had a jab.
The unvaccinated proportion has reduced from four weeks previously, when it was 31%.
And the area is still not meeting recommendations from the Scientific Advisory Group for Emergencies (Sage) which state four in five staff need to be vaccinated to provide a minimum level of protection against outbreaks.
Across the South East, 22% of eligible care home workers had not been vaccinated by April 11, while across England that figure stood at 21%.
The Government s plan would see older adult care home operators only able to use staff who have received a Covid-19 vaccination.
Workers with evidence of a medical exemption to the jab will still be allowed to work.
Health secretary Matt Hancock said: "Older people living in care homes are most at risk of suffering serious consequences of COVID-19 and we have seen the grave effects the virus has had on this group.
"Making vaccines a condition of deployment is something many care homes have called for, to help them provide greater protection for staff and residents in older people’s care homes and so save lives."
The idea has received support from some care home providers like Barchester Healthcare whose chief executive Dr Peter Calveley has implemented a similar policy for his staff.
He said providing safe care was the company's "paramount obligation".
However, Unison said the Government should give staff more time, tackle misinformation and put extra resources into areas with low take-up.
General secretary Christina McAnea said: “Too heavy-handed an approach could backfire badly. Some staff may simply up and go, leaving a poorly paid sector already struggling with thousands and thousands of vacancies in a terrible state.
“That could damage the quality of care for the elderly and vulnerable, and no one wants that.”
Cultural reasons as well as concerns over the AstraZeneca vaccine and anti-vax campaigns have led to some care home workers not taking up the vaccine, the National Care Association, which represents care providers, has said.
Staff, care providers, residents and their families are being urged to take part in the consultation, which is being run by the Department of Health and Social Care.