Jeremy Corbyn has vowed to scrap hospital car parking charges as an investigation found more than four in 10 NHS hospitals have increased their prices in the last year.
Some NHS trusts have doubled the cost of a stay for patients and visitors.
Freedom of Information data analysed by the Press Association shows that hospitals in England are making more money than ever from charging visitors, staff and patients.
Some 124 NHS trusts responded to the Press Association request for data on parking charges.
Of these, 53 (43%) said they had increased prices in the last year for visitors or staff, or both.
Meanwhile, 71 (57%) said they had not put up their prices.
Labour has pledged to abolish the costs while the Patients Association said people should not be “charged for being ill”.
"It's wrong to charge people to visit loved ones in hospital and the staff who care for them," Corbyn said.
"Labour will scrap hospital car parking charges," he added.
In some regions, prices have risen sharply, with trusts doubling the cost for some lengths of stay.
At Airedale NHS Foundation Trust in West Yorkshire, a stay of four to 24 hours cost £8 in 2017/18, up from £3.50 the year before.
Meanwhile, a stay of two to four hours now costs £5, up from £3. The trust made £1,287,322 from parking in 2017/18.
At Shrewsbury and Telford, which is subject to scrutiny over a series of baby deaths, an overhaul of parking charges has seen the cost of a five-hour stay more than double since October last year.
Visitors and patients used to pay £3.50 for a stay of between five and 24 hours, but this is now £8.
All stays under five hours have also increased, such as a 3.5-hour stay now costing £5, up from £3 previously.
Meanwhile, Alder Hey Children’s Hospital in Liverpool has scrapped its £2 flat rate for a full day and introduced a raft of new charges, tripling the cost of a stay longer than eight hours.
Parking for up to two hours now costs £2.50, while six to eight hours is £4.50 and eight to 24 hours is £6.
Lancashire Teaching Hospitals has also doubled the price of a stay of four to six hours over the last year, from £3 to £6. A stay of two to four hours has also jumped from £3 to £5.50.
However, the trust has reduced its one-hour stay from £3 to £2.50.
Some of the trusts that have put up prices are making millions every year from parking.
Frimley Health in Surrey, one of the highest earning trusts in England, made £4,452,481 from charging staff, patients and visitors in 2017/18.
This was up on the £4,126,587 it made the year before.
It has raised the cost of parking during each of the last two financial years. For example, a stay of under two hours used to be £3 but rose to £3.40 in 2017/18.
University Hospitals of Leicester made £4,421,862 from parking in 2017/18, a 13% rise on the £3,880,587 the year before.
In the last year, it has also increased prices across the board.
A two-hour stay for patients and visitors jumped from £2.50 to £2.80, while a four-hour stay rose from £4 to £4.40.
Meanwhile, North Bristol Trust, which made £2,565,595 from patients, visitors and staff in 2017/8, up on the £2,521,741 the year before, also hiked rates in 2017/18.
A stay of 20 minutes to two hours now costs £3.50, up from £3 the year before, while a stay of two to four hours is £5 (up from £4.50).
Data published by NHS Digital in October, analysed by the Press Association, showed that NHS trusts made more than £226 million in 2017/18 from parking, including penalty fines.
While NHS trusts in England still force people to pay for parking, the charges have been abolished in Wales and most of Scotland.
Some hospitals have defended their revenues, saying some or all of the money is put back into patient care or is spent on maintaining car parks.
Others claim their sheer size and the fact that they serve busy neighbourhoods means they take more revenue.
Shadow health secretary Jonathan Ashworth said: “These car parking charges are a tax on the sick. The next Labour government will axe them.”
Liberal Democrat health spokeswoman Judith Jolly said the charges amounted to “taxing the sick”, adding: “While it is clear to all that hospitals are struggling to cover their costs against a backdrop of financial pressures and overcrowding exacerbated by the Tories, that is not a green light to charge patients.
“Car park charges are not the answer to the pressures on our hospitals.”
Rachel Power, chief executive of the Patients Association, said parking charges generate revenue at a time when hospital finances are “under immense pressure”.
But she added: “Charges for car parking at hospitals are a charge on people who are unwell, levied on them because they are unwell.
“We believe that patients should not be effectively charged for being ill.”
Tom Sandford, director of the Royal College of Nursing in England, said: “Nursing staff work around the clock to keep patients safe – they should not be overcharged for doing their jobs.
“For staff working shifts public transport is often not an option, so nurses and support workers have no choice but to pay parking charges that rise year on year.
“Struggling hospitals should not try to make money from their staff. Their goodwill won’t last forever. Trusts should provide reasonable car parking with affordable charges.”
Dr Moira Fraser-Pearce, director of policy and campaigns at Macmillan Cancer Support, urged people to check what discounts were available for cancer patients.
She added: “Cancer can have a significant impact on people’s finances and if they have to pay to park at hospital in England, these charges can add considerably to this – especially for those undergoing treatment on a daily basis.”
Unison’s head of health Sara Gorton said: “Health employees whose shifts end after the last train or bus has gone, or who work in remote areas with little or no public transport, or out and about in the community, have no option but to use their cars.
“If the Government put more money into the health service, charges could be scrapped, and nurses, porters and their NHS colleagues would no longer have to pay through the nose simply to park at work.”
A Department of Health spokesman said: “We have made it very clear that patients, their families and our hardworking staff should not be subjected to unfair parking charges.
“NHS trusts are responsible for these charges and ensuring revenue goes back into frontline services, and we want to see trusts coming up with options that put staff, patients and their families first.”