MSPs are demanding a public inquiry into the massive Caltongate development following the warning that the controversial project could cost Edinburgh its World Heritage Site status.
Lothians Green MSP Robin Harper, Scottish Nationalist Shirley-Anne Somerville and independent Margo MacDonald are all urging ministers to order an inquiry rather than rubber stamp the 300 million scheme when it comes before them.
They say the investigation launched by Unesco into the future of the World Heritage Site status awarded to Edinburgh's Old and New Towns in 1995 should make everyone think again about the plans, which would see two listed buildings demolished to make way for a five-star hotel and conference centre with an entrance on the Royal Mile.
The Unesco review was sparked by concerns about the effect Caltongate and other proposed developments could have on the Capital's skyline. Mr Harper said: "We will have to live with whatever goes here for the next 100 years or more. It would cast a shadow on the planning system if there were not to be a public inquiry.
"If it then goes ahead, a lot of people might still be unhappy, but at least it would have gone through due process."
Ms Somerville said she believed people had not taken seriously enough the possibility of Unesco stripping Edinburgh of its World Heritage Site status.
She said: "This is an absolutely enormous development. There's no doubt something needs done with the gap site because it's such an important part of the city, but this development is not the way forward."
She rejected the idea that a public inquiry would mean such a major delay that the project would effectively have to be abandoned.
Ms MacDonald said whether or not the World Heritage Site had brought any benefits to Edinburgh, losing it would be damaging.
The call for a public inquiry comes as councillors prepare to consider the plans once again tomorrow. A blunder by officials meant objectors were not given their statutory 14 days to comment on the council's decision earlier this year to approve the scheme.
The planning committee is expected to confirm its original approval, but the applications must then go to ministers once more.
And although they gave the green light last June, they will have to decide whether to rubber stamp the approval again, call the plans in to decide themselves, or hold a public inquiry.
A spokesman for developer Mountgrange said it had spent years consulting the council, Historic Scotland and the community. "We feel we have met the required standard in terms of the economic and social case and dealt with the issues to do with heritage. And up till now the council and the government have agreed with that position. We see no need for a public inquiry."