Patients and their families at East Sussex hospitals face a 250 per cent rise in parking charges.
Cash-strapped health officials plan to increase fees from £1.20 a day to £3.
The move would affect Eastbourne District General Hospital, the Conquest Hospital in Hastings and All Saints in Eastbourne. All are run by East Sussex Hospitals NHS Trust, which is facing a £5.2 million overspend this year.
Eastbourne Tory MP Nigel Waterson has written to trust chief executive, Annette Sergeant, to express his concern over the proposals, saying any increase would greatly affect the many elderly people in Eastbourne.
He is urging the trust's board not to press ahead with the option, one of several under consideration. The move will not affect staff.
Mr Waterson, co-chairman of the all-party group for older people, said: "I know many of my pensioner constituents find even the existing charges difficult.
"A rise to £3 would be wholly unacceptable. These higher charges are especially tough on people visiting a loved one who has a long-term condition."
The trust is in financial straits and a 38-point recovery plan has been drawn up to counter the predicted £5.2 million overspend.
This includes shedding some management and administration jobs, a review of agency nursing and how medical supplies are purchased.
Mr Waterson, in his letter to Mrs Sergeant, said: "I know that due to underfunding the trust is having to balance its books but I would urge you and your colleagues to look elsewhere. Visitors are a real lifeline for your patients."
The trust stressed no final decision has yet been taken and a number of options are under consideration.
Director Andrew Stenton, in overall control of the trust's estates and facilities, said: "Car parking charges have not been raised at either the DGH or Conquest hospital sites since 2000, and consequently our current charges are now out of step with those charged locally, in either council-operated or private car parks.
"This is becoming an issue for us as we are finding that the hospital car parks, especially at Eastbourne, are being used as a park and ride facility, with drivers parking at the hospital, often all day and then travelling by public transport into town.
"Different charges are also in operation at the DGH and the Conquest, and as part of one trust, uniform parking charges now need to be introduced.
"Although there is parking for more than 250 visitors at each hospital site, we are aware that it can often be difficult to park at the hospitals and our staff do everything possible to try and assist visitors and patients with finding a space. "
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