Trade union Siptu has been told to provide a business and management plan for a proposed heritage centre at Liberty Hall, the office tower that the union hopes to redevelop.
The union will have to address any conflict between the heritage centre and the "potential perceived negative impacts this building may have on the tourist sustainability of the city's Georgian quarter", Dublin City Council has said.
The council also wants further information on the proposed 19-storey building for the site. Further justification of the design is required, it said, and it also wants more details on the "innovativeness of the proposed material finishes" to the building.
The original building was constructed in 1965 and, at 17 storeys in height, is Dublin's second-tallest building.