Staff at Mid Yorkshire Hospitals Trust paid almost a million pounds to park at their place of work last year.
Figures which show the rising cost of parking at Pinderfields, Pontefract and Dewsbury hospitals have been released under the Freedom of Information Act.
In 2011-12, Mid Yorkshire staff collectively paid £650,233 for their workplace parking permits.
The figure rose to £911,125 the following year and reached £991,369 in 2013-14.
The cost of parking for employees rose by four per cent at the end of March - twice the rate of inflation at the time - while most NHS workers were awarded just a one per cent pay rise.
Adrian O’Malley, who represents members of public sector Unison at the trust, said: “We have suspected for a long time that this is just money making on behalf of the trust.
“There was a big rise in parking charges two years ago and it’s going to keep going up and up. It was increased by four per cent this when NHS staff are only getting a one per cent pay rise.”
At Dewsbury and District Hospital, income from parking charges goes into the trust’s own funds.
But at Pinderfields and Pontefract hospitals, the revenue goes to Consort Healthcare, a private company which built the hospitals under a Private Finance Initiative.
Mr O’Malley said: “People shouldn’t have to pay to park at their place of work. And this money isn’t being ploughed back into patient care. It’s going to shareholders.”
For patients and visitors, some parking charges rose by up to 20p at the end of March.
The cost of a one-hour stay for patients and visitors remained at £1.30. A two-hour stay rose from £2.70 to £2.80, and stays of up to four hours went up by 10p to £4.10.
The charge for parking for between four and 24 hours also rose from £6.70 to £6.90.
Mid Yorkshire listed its total income from patient and visitor parking and from charging other organisations to park at its hospitals as £735,760 in 2011-12, £385,158 in 2012-13 and £405,579 last year.
It could not confirm how much of those amounts, or the income from staff car parking permits, went to Consort Healthcare.
Mid Yorkshire said parking was included in its repayments to Consort Healthcare as part of the PFI contract.
The trust’s overall monthly repayments to Consort totalled more than £3.8m in March alone.
Iain Brodie, general manager of facilities at The Mid Yorkshire Hospitals NHS Trust, said: “Following a review of staff car parking charges in 2012, a small increase was implemented in 2012-13 and a further increase was applied in April this year.
“Our staff car parking charges vary by pay grade, with those on a higher grade paying the most.
“The current rate equates to an average of around £1 a day for our staff to park.”
Information on parking concessions can be found on the trust’s website www.midyorks.nhs.uk