The Western Health Trust is to extend its paid-for parking spaces by more than 250 at Altnagelvin Hospital.
The move has been criticised by the trade union, Unison, which says it will penalise low-paid workers as well as patients.
The Western Trust said it was necessary because of increasing demand for parking spaces.
Paid spaces will increase to 405, but the remainder, 1,271 spaces, will continue to be free.
Sara Groogan, Western Trust Director of Performance and Service Improvement, said: "The demand for car parking at hospitals continues to grow year on year.
"Due to the high volumes of traffic, measures need to be put in place to improve traffic management arrangements, utilisation of parking spaces, and access by patients, carers, visitors and staff."
She said that such measures would require investment, and that meant that it was necessary to generate income from car parking.
However, Trevor Lucy, from the Foyle Branch of Unison, criticised the move:
"I'm not sure if there will be very much income generated from this," she said.
"The real issue is that we do not have enough car parking spaces."
He also said he was concerned at the lack of exemptions for low paid workers.
The proposal would mean charging for 89 parking spaces at a secure car park on the south side of the hospital, and also at 183 parking spaces at the outpatient car park on the north side of the hospital.
There would also be eight extra disabled parking spaces at the main outpatient entrance.
The Western Trust said it would consider offering free car parking "in discretionary situations".
The trust also proposes to increase car parking charges from 60p to 70p per hour.