Some older people in care homes are being asked to pay more than £100 a week extra in fees to cover the costs of coronavirus.
Age UK said residents who pay their own fees are facing the bills to pay for protective gear and rising staff costs.
It adds “insult to injury” for people who have “been through the mill” during the pandemic, the charity said.
The government said it provided £600m for infection control in care homes and £3.2bn for wider council services.
Care home residents who fund themselves have effectively subsidised the care system for many years, paying far more for their support than those funded by their local authority.
Age UK says on average these residents are charged just over £850 a week, and some are now seeing their fees rise by 15%.
It is not clear how many care homes have asked self-funding residents to pay more.
There are 400,000 people estimated to be living in care homes in England, with 167,000 believed to be self-funders and 45,000 part self-funders.
Caroline Abrahams, director of Age UK, said older people and their families have “been through the mill” in recent months as outbreaks occurred in one in three care homes.
“It is adding insult to injury that after going through so much, some residents who pay for their own care are now facing a big extra bill – on top of already expensive fees.”
She called for government to meet the extra costs of the pandemic, saying that otherwise there was a risk that some could fold and leave their residents homeless.
During the pandemic, many care homes have spent hundreds of thousands of pounds of protective equipment to stop the spread of Covid-19 between staff, residents and visitors.
They have also faced extra costs for agency staff when employees are off sick or isolating.
In total, the Local Government Association (LGA) and directors of adult social care estimate that providers face potential additional costs of £6.6bn between April and September.
“People living in care homes should not be penalised in this way,” said councillor Ian Hudspeth, chairman of the LGA’s community well-being board.
He said the way self-funders subsidised the system was already unfair and should be addressed as part of the long-term reform of the social care system.
But he said councils were helping care home providers with the extra costs “to the best of their ability”.
To support their work during the pandemic, local authorities have been given £3.2bn by the government, which also announced a £600m infection control fund for care homes.
The Department of Health and Social Care said it would keep future funding needs under review, but would not confirm that it would provide more money to councils.
It said it would work with local authorities to ensure the funding is distributed fairly and reaches front line services.
“We recognise that this pandemic is creating significant challenges for care homes and that extra support is needed to care for residents,” a spokesman said.
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