People from outside the EU who seek help from the NHS are to be charged 150% of what the operation costs the health service, ministers have announced, in a bid to deter so-called "health tourism".
Under the new plans plans, non-EU patients receiving procedures will pay 50% more than what the operation cost the NHS.
This means having a baby will set them back £2,244, having a hip operation will cost £12,865 and cataracts surgery would cost £2,800.
But Dr Mark Porter, chairman of council at the British Medical Association, said there were "question marks" over whether the proposals could work.
The Department of Health (DfH) said that visitors and migrants can currently get free NHS care soon after they arrive in the UK, leaving the health service "open to abuse".
It is now asking the NHS to "clamp down" by identifying these patients more effectively so costs can be recovered.
NHS Trusts that fail to identify and bill "chargeable" patients could face financial sanctions, it said.
Health Secretary Jeremy Hunt said: "We have no problem with international visitors using the NHS as long as they pay for it - just as British families do through their taxes.
"These plans will help recoup up to £500 million a year, making sure the NHS is better resourced and more sustainable at a time when doctors and nurses on the frontline are working very hard."
The new measures are expected to come into force by next spring, with ministers hoping that improved IT and administration systems will dramatically increase the numbers of patients identified as not being eligible for free care.
The DfH has agreed to pay Trusts 125% of the cost of treatment received by EU nationals, in the hope that they will be encouraged to report more cases.
The government will then be able to reclaim money back from other member states under reciprocal agreements already in force.
Dr Porter said: "Anyone accessing NHS services should be eligible to do so but a doctor's duty is to treat the patient that's in front on them, not to act as border guard.
"Any plans to charge migrants and short term visitors need to be practical, economic and efficient and must not jeopardise access to healthcare for those who need it.
"Without more detail, there are question marks over whether or not these proposals will be workable and if the NHS has the infrastructure and resources necessary to administrate a cost-effective charging system."
He added: "Plans to fine hospitals who fail to recoup costs would see them punished twice over, to the detriment of other services.
"Above all, it's vitally important that these proposals don't have an impact on the care patients receive and that sick and vulnerable patients aren't deterred from seeking necessary treatment, which can have a knock on effect on public health."Suggest a correction