Jersey's Environment Minister has ordered a Public Inquiry into plans for new housing at the Ann Street site and the Mayfair Hotel in St Helier.
Deputy John Young has signed a Ministerial Decision saying he will not make a decision on either development until an inquiry has been held.
These developments, were they to be carried out, would be likely to have a significant effect on the interests of a substantial part of the population of Jersey.
An independent Planning Inspector will be appointed, and members of the public will also be consulted on their views.
Plans to convert the site into 300 affordable housing units were put forward by Dandara on behalf of Andium Homes in January.
It would mean another substantial housing development in an area of town that is already undergoing significant regeneration; Andium Homes has another two projects ongoing in the area - one of them is the former Gas Place site, where 122 flats are being developed, and the other is at Anne Court.
A separate project, approved last year, will see a 122-bedroom Premier Inn and 145 apartments developed on Bath Street.
In July last year, plans for 195 apartments were also approved on the former Play.com warehouse site, behind the St Helier Co-op Grande Marche.