According to Icomos (the International Council of Monuments and Sites), 3XNielson's proposals for a new Museum of Liverpool on the historic waterfront site will 'severely harm the iconic status of the Three Graces'.
The body had urged Liverpool City Council not to back the scheme to allow UNESCO's World Heritage Committee time to review the £63 million scheme - labelled the Fifth Grace by Merseysiders, after the collapse of Alsop's Cloud.
However, following Tuesday's decision, Icomos is now demanding a public inquiry into the project, a move which could delay the plans by years.
Among the list of the organisation's 'grave concerns' about the development is the scale and prominence of the museum.
In a statement sent to Liverpool Council at the beginning of the month, Icomos claims that a fourth building on the pierhead site 'of such architectural pretension shows a fundamental misreading of the precious nature of the existing group and of the rationale for the inscription of the World Heritage Site- and will undermine and diminish the symbolic significance of the Three Graces'.
The report goes on: '[The proposed building] is an extreme manifestation of the contemporary tendency to see buildings as sculpture rather than architecture, and to seek to justify this self-indulgent approach by the use of written terminology that- does not stand up to critical examination.'
Even so, the Danish practice still hopes work can begin on site in April next year.