A parking firm has been criticised for issuing penalty notices to hospital staff, despite them paying a monthly fee to use the facilities.
ParkingEye said there had been a small number of cases where vehicles were not correctly registered at United Lincolnshire Hospitals Trust (ULHT).
However, Bryn Jones, from Unite, said the system run by ParkingEye was not fit for purpose.
ULHT confirmed it was working with the firm to resolve any issues.
ParkingEye introduced the new automatic number plate recognition (ANPR) system in November 2018 when it took over the contract.
At the time, ULHT claimed it was "highly accurate, fair and transparent".
But problems with the system meant fees were temporarily waived for visitors and patients, before they were reintroduced in January.
ParkingEye said it was working to resolve any problems and had rescinded wrongly issued notices.
However, Mr Jones said some hospital workers had received multiple penalty notices in error, claiming problems with the ANPR system were continuing.
He said some staff were having to spend hours gathering evidence to appeal after working long shifts on the wards.
This had led some to consider leaving ULHT to work at other hospitals, Mr Jones added.
A petition has also been launched calling for the system to be scrapped and the old barrier system brought back.
ULHT, which has hospitals in Lincoln, Boston, Grantham and Louth, said it was aware of staff being issued with penalty notices and advised them to appeal.