Unesco, the body that polices heritage sites around the world, has been urged to intervene over the Caltongate project by another major cultural watchdog, the Paris-based International Council on Monuments and Sites (Icomos).
Campaigners opposed to the project, including writers Irvine Welsh and Alexander McCall Smith, are also contacting MSPs and asking them to raise the issue at Holyrood.
Dr James Simpson, of Edinburgh-based Simpson & Brown Architects and UK vice president of Icomos, said strong representations have been made to Unesco but that talks were at an early stage.
The plans by development consortium Artisan Real Estate Investors for two hotels, shops and homes at the Royal Mile have been criticised since being approved by Edinburgh City Council in January.
Mr Simpson said he believes the development is wrong for the city and added that protecting the World Heritage Site was a matter of national interest.
He said: "It [the granting of approval] is what it does to Scotland's reputation internationally if its World Heritage Sites are not managed to a high standard.
Mr Simpson added: "I am contacting MSPs. It should be raised in the Scottish Parliament."
He said that one councillor described the project as "not hideous enough" to be rejected when the plans were being approved. "That reflects and highlights the fact that there is no aspiration."
He said an Icomos UK committee meeting is due and Caltongate will be top of the agenda, adding: "Icomos has contacted Unesco, but I don't know at this stage how Unesco has responded."
The hotels are expected to be part of a wider mix built around a pedestrian friendly urban centre. The plans include open public spaces with independent retailers, restaurants, homes and offices. A separate earlier development prompted Unesco to send previous developers for the site, Mountgrange, to the drawing board.
Mountgrange went bust before they could develop plans in response to Unesco's requests.
Artisan developed its own plans for the area, which it claims will create 2000 jobs.
World Heritage Site status is seen as a major boost for tourism and the economy.
Dresden in Germany was deleted from Unesco's World Heritage list in 2009 because of a bridge that was judged to have undermined its "outstanding universal value".
The council and Edinburgh World Heritage said earlier in a joint statement: "Whilst Edinburgh World Heritage advised that the proposals would have a minor negative impact on the World Heritage Site, it was made clear that this of itself would not warrant inclusion on the World Heritage 'in danger' list or threaten its status as a World Heritage Site."
Euan Leitch, of the Architectural Heritage Society of Scotland, said the plans were not appropriate for Edinburgh's Old Town.
Icomos develops best practice in the conservation and management of cultural sites, and has a special role as adviser to the Unesco World Heritage Committee on cultural World Heritage sites.
A spokesman for Artisan said: "Our planning consents followed more than 18 months of in-depth consultation with local communities and stakeholders.
"We have listened to, and taken on board, a huge variety of views and opinions on the development of the site, and heard impassioned arguments relating to its unique importance, setting, heritage and community. We feel our proposals reflect this varied, dynamic and open consultation process and we feel we now have a proposal which shows a genuine understanding of the area's celebrated community and civic context."