Around 800 people turned out at a public meeting in Llanidloes to oppose any plans to close the town's community hospital.
The hall was packed out for the public meeting
An action group has been set up to fight any such proposal being put forward as part of a wider plan to reorganise health services in the area.
A petition of more than 4,500 names was presented to Powys Local Health Board representatives.
The board, which meets later this month, said no decision had been made.
Brecon and Radnor Community Health Council (CHC) warned in October 2005 that hospitals in Llanidloes, Bronllys near Brecon, and Builth Wells could be affected by the health board's then budget deficit of £6.7m.
The health board has said the financial situation may lead to a "short-term rationalisation of beds".
Speakers at the meeting on Monday evening called on the health board to reconsider making savings at the expense of their local hospital.
Llanidloes town councillor David Jones, one of the chairs of the meeting, said: "There has been no investment in the hospital over the last few years. We were promised an investment of three-quarters of a million [pounds]. We saw nothing.
Senior figures from the local health board were invited speakers
"Earlier on this year they said that there was £150,000 going to be spent on refurbishment at the hospital. We've seen absolutely nothing."
Mr Jones said the community was "very concerned about the future of health care and health provision in the Llanidloes area".
He said changes at the hospital, included a drop in the number of beds from 30 to 18, led him to believe the local health board had an agenda to close the hospital.
The health board said the future of the memorial hospital was being considered as part of a review of healthcare across the county.
A statement on behalf of the board said: "No decision has been made on the future of Llanidloes Hospital, and discussions are due to be held shortly."
The health board's next meeting is on 27 September.