Powys Council says it can no longer afford to maintain the listed Victorian market at Newtown.
Hundreds of people have signed a petition calling on a council to keep an historic Victorian market hall open.
Powys council cannot afford to maintain the Grade II-listed indoor market at Newtown and said it had received a "good response" from potential buyers.
But if the building is sold traders want officials to guarantee the market's future.
The council's ruling board met behind closed doors on Tuesday and deferred a decision about its future.
The local authority first considered selling the market hall to the private sector is 2005.
Newtown mayor Sue Lawson, who used to run a stall inside the market with her mother, said she wanted it to remain open.
Traders are uncertain of their future if the hall is sold
"It'll be a shame if it closes as a market," she added.
"I would like to see it remain and some money spent on renovating and modernising it. The market hall contains businesses which have been there for decades and I don't know what they'll do if it closes."
Stallholders fear sale of the building could spell the end of its traditional market role, which dates from the 1870s.
Andrew Comer, chairman of the Montgomeryshire branch of the Market Traders' Association, runs a hairdressing salon in the hall.
He said an important part of the town's heritage was at stake.
Conservative prospective parliamentary candidate Glyn Davies supports the campaign to keep the market open.
He said: "Market traders and the market hall are part of the cultural heritage of Newtown, and I hope the council will ensure it continues when it sells the building."
Powys council said it advertised for expressions of interest and had received a good response.
Following Tuesday's meeting, a spokesman said councillors would wait until a decision had been made about two proposed supermarket sites before considering the market's future.
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