Documents were requested by the Park and Woodlands Heritage Group relating to the project at Park Quadrant, where Expresso Property plans to develop 111 flats.
The A-listed Park Circis is part of a planned development created by architect Charles Wilson in the 1850s.
Heritage campaigners are concerned the iconic site could be affected the conservation of the area.
The Group were seeking to determine whether the council has taken steps towards preparing a Conservation Area Appraisal (CAA) for the area.
However, after being told there was no such documentation, the council admitted that an early draft did exist but disclosing the information would not be in the public interest.
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Sandy Steven, a spokesman for the Park and Woodlands Heritage Group, said: "We welcome the Information Commissioner's intervention and look forward to the outcome of the investigation.
"It is astonishing that Glasgow City Council could possibly think that the information we seek is not in the public interest. There are 24 conservation areas in Glasgow, most of which are the subject of Conservation Area Appraisals containing guidelines on future development.
"It is hard to understand why the Park area, which is among the city's most important pieces of historic urban design - of both national and international significance - is not protected by a Conservation Appraisal.
"It is of the utmost public interest that the conservation of this area is seen to be under close control. It is also important that the conservation guidelines be transparent and available for all to see so that there is no doubt as to what is considered acceptable development of this unique cityscape."
Originally, the developer planned to build 149 flats on the site.
Tom Johnstone, another spokesman for the group, added: "The fact that Expresso originally wanted to build as many as 149 flats on this site shows that the company clearly has no understanding of the Park area and its special character."
(LM/CD)
