Concerns over the prospect of parts of the Assembly Rooms being given over to shops and a restaurant are mounting just days before councillors make a crucial decision on the fate of the George Street building.
Veteran producer Guy Masterson, actors Simon Callow and Brian Cox, comedians Johnny Vegas and Jo Brand, and Scottish Opera's general director Alex Reedijk are among those to have recorded special video messages attacking the plans, which will be discussed by councillors on Wednesday.
Historic Scotland, the Architectural Heritage Society of Scotland and the Cockburn Association have all raised fears about the impact of a 9.3 million overhaul, which will see the building close for around 18 months.
The city council has been warned that the project will see the building become too commercialised and its historic character damaged.
Assembly Theatre, which has used the building during the Fringe for 30 years, has unveiled a protest website and a Facebook campaign attacking the council's plans for the "iconic" A-listed building, claiming it will be "severely damaged".
The promoters are also warning the "magical" atmosphere of the Fringe venue will be lost forever if the current scheme goes ahead and have urged the council to go back to the drawing board.
However the council has insisted the changes are needed to guarantee the building's future and ensure it is used all 52 weeks of the year. It has also threatened to bring in another promoter to run Fringe shows there.
The council's plans for the Assembly Rooms, built in 1784, would see two new shop units created on the ground floor facing on to George Street, along with a year-round restaurant to the rear of the building.
However Historic Scotland has demanded a more sympathetic approach to the plans for the revamp, while the AHSS has raised concerns about a loss of public access.
Assembly Theatre's campaign website also states: "We don't believe the public have been properly informed about this development or the impact it will have both architecturally and on the current users."
Mr Masterson said: "The smaller spaces are where we, as producers, take the risk. Losing them would turn the Assembly into a purely commercial entity without a soul."
William Burdett-Coutts, artistic director of Assembly, said: "I've been trying to get the council to listen to us for the last year, but have made no progress at all."
Steve Cardownie, the council's festivals and events champion, said: "This is pure scaremongering.The refurbishment of the Assembly Rooms will guarantee the building's future as one of the most sensational events venues in the city."