The George Street venue is closed for 18 months to allow the 9.3 million scheme to go ahead, despite a campaign organised by Assembly Theatre, the firm that runs a Fringe venue from the building.
Joshua Miller, of the George Street Association, said: "It is a fantastic venue when used. The rest of the year however, we support the opportunity to have more events, create more retail space and retain the majority of performance space upstairs."
Lesley Williams, of the Edinburgh Convention Bureau, said: "For the 400 to 600 delegate market, facilities in Edinburgh are limited. Once the EICC is booked, there are no mid to large venues in the city centre.
"By having a newly refurbished Assembly Rooms as part of Edinburgh's cultural offering, we feel it is essential in maintaining Edinburgh's reputation as a conference city."