It also voices concern at the "apparent lack of public awareness" until recently about the scheme, which includes converting the lower floors of the building to shops and a restaurant. Mr Harper said the Assembly Rooms was one of Edinburgh's historic, architectural and cultural assets and he drew attention to the campaigners' petition at www.savetheassemblyrooms.com, which now has around 6000 signatories.
He pointed out that if agreed at tomorrow's full council meeting, final approval of the plans would still have to be given by ministers.
Critics say the revamp will destroy the venue's integrity.