A migrant charity is warning thousands of people could end up in debt and facing "severe poverty" as the healthcare levy applied to migrant visas has almost doubled.
From 6 February, the Immigration Health Surcharge rises by 66% for those applying to come to the UK or extend their visas.
It means the standard rate of £625 will rise to £1,035 a year, and applicants are expected to pay upfront in conjunction with their visa fees.
A reduced rate applies to visas for students, those under 18 and young adults on youth mobility schemes, which are also set to rise from £470 to £776.
Mary, 44, who did not want to give her real name due to fear of judgement, is an assistant nurse with two young British children.
She came to the UK in 2009 from Nigeria and has to renew her limited leave to remain visa in May.
She says the increase to the immigration health surcharge is simply "unaffordable".
She will be expected to pay £2,587 to obtain access to NHS care for the duration of her visa, on top of around £1,048 in Home Office fees for processing her visa application.
'I have to go into debt'
"I cannot afford it. It's going to be stressful, the fear of how to get the money is my problem now and I won't be able to satisfy my children's needs," says Mary.
She says due to the cost of living crisis, she may have to sacrifice her children's basic needs like gas and electricity, so she can pay the fees.
"I have to go into debt. It's just stressful, especially when you have health challenges and you have to think about how you are going to survive with your children," she said.
There is a refund scheme in place for some applicants, which also applies to most people who work in the NHS.
There are different ways to get money back though, depending on the visa and the job. For example, those who do not have a Tier 2 general visa can only apply for a refund six months at a time.
As for Mary, because she is a nursing assistant on a zero-hour contract, she says she is not eligible.
Nicola Ranger, chief nurse at the Royal College of Nursing, says it is "unacceptable" that those who are qualified for the refund "will have to wait six months before being eligible" for a refund.
But she says she is also concerned about the impact it could have on migrants accessing the NHS.
"It could discourage migrant workers and their families from maintaining their visas, creating a risk that more patients are subject to the NHS charging system, and deterred from accessing the health care they need," she said.
An individual on the limited leave to remain scheme can pay on average about £4,000 every two and a half years to renew their visa, according to migrant charity Praxis, who are calling on the government to abolish the added healthcare fee.
A spokesperson for the Home Office said that while it recognises the migrant contribution to the country, it mandates "a financial contribution from those using public services", which includes the NHS.
They added: "The new rate reflects increases in healthcare expenditure and better reflects the NHS use by migrants, who are provided with near-comprehensive access to health services in return.
"Applicants for the health and care visa, including international nurses, are exempt from the surcharge."