UNISON has highlighted the wide disparity between how much it costs NHS staff in different parts of England to drive to work.
Research by the UNISON union found there was a wide variety in what health workers had to pay to take their car to work and NHS Staff are being up to £90 a month just to park at their workplace.
The union used freedom of information act request to survey 199 NHS trusts revealing which forced their workers to pay and which allowed them to leave their cars for free.
UNISON revealed the most expensive was the Royal Free NHS Trust in London, where it costs full-time staff £85.38 a month to park, with those working for the Royal Liverpool and Broadgreen University Hospitals Trust, have to spend £79.50 a month.
Most NHS trusts operate a flat-rate payment system regardless of a staff member's income, but some offered discounted parking for those on lower wages, while others did not charge their employees to park at all.
UNISON's head of health Christina McAnea said: "Health staff are struggling to get by on a pay rise well below the cost of living and these extortionate fees are an extra tax on their wages".
"Many NHS staff work shifts so they have to drive because they can't get buses or trains in the middle of the night. Health workers in rural areas, where public transport is virtually non-existent, are entirely dependent on their cars to get to work.
"Others have to fork out for expensive permits with no guarantee of a space when they get to work".
Ongoing pay restraint is hitting healthcare professionals hard and UNISON compared this extra charge to a "work-tax".
A student nurse in Nottingham, meanwhile, said: "I may not be able to continue with my studies. I already spend £60 a week in petrol to get to the hospital, plus £9 A day for parking."