People struggling to get a new library built in Lewes fear the on-off project could be put on hold again.
Campaigners who have been told they must raise £500,000 for the new library fear East Sussex County Council wants major alterations to the building's design.
The council last month pledged £1.9 million for the project but has still not agreed to buy the land at Lewes House in High Street.
The authority is locked in negotiations with landowner Lewes District Council, with a deadline for the sale looming next Thursday.
District council leader Ann de Vecchi said: "Until we know the county council is actually going to buy the land, we are in limbo. It wants more flexibility.
"It has made a commitment to build the library but not necessarily to the same design."
The district council has twice extended the deadline for selling the land because of uncertainties over funding the project.
Plans for the library were unveiled to acclaim last spring but the county council put it on hold a few months later saying it could not afford the scheme.
The cash-strapped authority agreed to put the £1.9 million into the library last month but only if campaigners made up the shortfall.
A further £500,000 grant from the Arts Council is to pay for a regional literature centre.
The Lewes Library Friends, which launches its campaign to raise the missing £500,000 on Saturday, said it was concerned about the hold-up.
Spokesman Lyn Donbroski said: "We have shown our good faith in saying we will try to raise this money.
"We are looking forward to the county council fulfilling its part of the bargain."
The library would house a book and music library and a Citizens' Advice Bureau.
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