The British Medical Association (BMA) has demanded car park charges are scrapped at Welsh hospitals, claiming they are "a tax on the sick".
Welsh Assembly Government figures show NHS trusts took £5.4m last year, but that does not include private firms running car parks on their behalf.
Hospitals say the money is needed to cover maintenance and security and any surplus goes to patient care.
Health Minister Edwina Hart will make a statement on charging reform next week.
Dr Richard Lewis, Welsh secretary for the BMA, said: "Charging people to park at hospitals is an indirect tax on healthcare.
"These days, the vast majority of people who attend hospital clinics do so by car.
"Often, these people have to attend several times during treatment and the costs mount up. It's iniquitous that they have to pay to access hospital care.
"Patients and visitors will be shocked to learn that NHS trusts are making thousands of pounds a year, without any significant benefits.
"Wales should stop this tax on the sick."
The figures were obtained by the BMA in a written response from Mrs Hart to Conservative Jonathan Morgan, who called the charges a "rip-off" and "totally unacceptable".
"We must ask ourselves whether we want a healthcare system free-at-the-point-of-use or not," he added.
"They are also an added tax on staff who, in many remote parts of Wales, simply have no alternative to the car."
The figures show Swansea NHS Trust collected £1,483,706 in charges in the last financial year.
TRUST PARKING INCOME
Bro Morgannwg: £579,303
Cardiff and Vale: £680,581
Conwy & Denbighshire: £423,793
Gwent Healthcare: £973,808
North East Wales: £571,171
North Glamorgan: -
North West Wales: £100,000
Pembrokeshire and Derwen: £51,800
Pontypridd & Rhondda: £349,825
Powys LHB: -
Figures do not include income received by private companies providing services at hospitals
Where no figures are included, the trusts do not charge for car parking
Source: Welsh Assembly Government/Estate and Facilities Performance Management System.
Gwent collected £973,808 and Cardiff and Vale £680,581 although that did not include income from the car parks at the University Hospital of Wales and St. David's which are managed by a third party.
Three trusts, North Glamorgan, Powys and Velindre do not charge for car parking.
A spokeswoman for Swansea NHS Trust said nearly half the money collected was spent on staffing the car parks, maintenance and night-time security.
"The remaining £766,063 was ploughed back into patient care," she added.
"Care has been taken over charges for car parking in Swansea, to ensure that those who need to come to hospital regularly pay as little as 72p a day."
Simon Williams of Cardiff and Vale NHS Trust said: "The trust introduced a car parking strategy following consultation with relevant parties including both Cardiff and Vale of Glamorgan community health councils and trade unions.
"The charges are used for on-site security and patrolling of car parks, improving signage and upgrading facilities across sites."
All revenue received from parking at the University Hospital of Wales is retained by the private finance initiative provider Vinci Park (Cardiff) Ltd and no revenue goes to the trust, a spokeswoman said.
Julie Evans, 43, a ward manager at University Hospital of Wales, backed the BMA's stance.
"It's awful because you get people and their relatives who are long-term patients and that is their main concern sometimes.
"A lot of them don't have much money or are on social security. When people are ill it's the last thing you want to think about."
She said parking charges for staff added up over a year, and although staff could park more cheaply, if the staff car parks were full they had to pay the same amount as visitors, which was around three times as much.
An assembly government spokesperson said Ms Hart was aware of concerns over the cost and was commited to reform charges for hospital parking.
"Ms Hart will make a statement on how she intends to take that forward to improve the situation for patients, visitors and staff next week."