Trade union GMB said it is "sickening" that nurses, midwives and cleaners in many trusts across the country have had to pay to park at their place of work.
It has called on ministers to scrap parking charges for workers altogether.
NHS Digital data shows the University Hospitals of North Midlands NHS Trust made around £3.9 million through parking charges and penalty fines between April 2019 and March 2020. Of that, £3 million was paid by patients and visitors, and £852,438 through charging staff to park.
The Royal Wolverhampton NHS Trust made around £2.9 million through parking charges and penalty fines in the year to March 2020. Of that, £2 million was paid by patients and visitors, while £856,233 was raked in through charging staff to park.
The data shows Sandwell and West Birmingham NHS Trust made around £2.4 million through parking charges and penalty fines. Of that, £1.7 million was paid by patients and visitors, while £736,731 was through staff parking.
The Dudley Group NHS Foundation Trust made £1.6 million through parking charges and penalty fines during that time. Of that, £1.1 million was paid by patients and visitors, while £539,981 was from staff paying to park.
Data shows the Walsall Healthcare NHS Trust also made around £1.6 million in that period – with £1.1 million paid by patients and visitors, and £467,989 by staff parking.
Across England, NHS trusts raised £289 million from parking charges – nearly a third of which came from staff parking, generating £90 million over the year.
The figures represent the gross income earned by the NHS and do not take into account its own costs for providing car parking.
Trade union GMB said charging NHS staff to park at work is "disgraceful". Rachel Harrison, the union's national officer, said: "Government cuts have inflicted a heavy toll on the NHS, but trusts should not be clawing that cash back by charging the people we rely on to keep us alive."
The Government announced last year that it would cover the costs of providing free car parking to NHS staff working in hospitals during the coronavirus pandemic. However, it said the scheme would end in all but "certain circumstances" as the pandemic eased over the summer.
Ms Harrison added that it was "sickening" to see workers forced to shell out for parking again as some trusts reintroduced charges for staff. She added: “Ministers must now support our healthcare heroes by enforcing free hospital staff parking and scrapping plans to reintroduce charges once the pandemic ends."
Patients' rights campaigners the Patients Association said while billing people to park at NHS car parks is a "charge on people who are unwell," it provides much-needed income for trusts at a time when their finances are under pressure.
A spokesman for the Department of Health and Social Care said: "In March, the Government committed to making hospital car parking free for NHS staff for the duration of the pandemic and is providing additional money to NHS trusts to cover the cost of implementing this.
"Any surplus income generated from hospital car parks not used to fund the provision of car parking, such as security and maintenance, must be reinvested into frontline care."