Patients could be made to show their passports when they use hospital care in England under new rules introduced by the Department of Health.
Those accessing new treatment will be asked questions about their residence status in the UK reports BBC.
Patients may need to submit passports and immigration documents when this is in doubt, the department said.
Hospitals will also be able to charge short-term visitors from outside Europe 150% of the cost of treatment.
The department said the new rules came into force on 6 April for overseas visitors and migrants who use NHS hospital care in England.
Primary care and A&E care will remain free.
There will also be financial sanctions for trusts which fail to identify and bill patients who should be charged, it said.
The plans are part of a crackdown on so-called “health tourism”.
Andrew Bridgen, the Tory MP for North West Leicestershire in the last Parliament, told daily Mail: “This is not the International Health Service, it’s the National Health Service.
“Non-UK nationals seeking medical attention should pay for their treatment.
“The NHS is funded by UK taxpayers for UK citizens and if any of us went to any of these countries we’d certainly be paying if we needed to be treated.”
Most foreign migrants and overseas visitors can currently get free NHS care immediately or soon after arrival in the UK but they are expected to repay the cost of most procedures afterwards.
The charges are based on the standard tariff for a range of procedures, ranging from about £1,860 for cataract surgery to about £8,570 for a hip replacement.
Non-UK citizens who are lawfully entitled to reside in the UK and usually live in the country will be entitled to free NHS care as they are now.