Local businesses, English Heritage and Prince Charles have squared up to the Corporation of London and Railtrack over the proposed development of the site.
Community groups fear that the corporation and Railtrack are planning to extend the Square Mile with a swath of offices. Railtrack has attempted to appease the protesters by committing its future architect to consult a range of interest groups.
Hadid and KPF have been joined on the shortlist by Rotterdam-based practice Kees Christiaanse and a joint bid from EDAW and Rafael Viñoly. The four beat off competition from well-known architects including Norman Foster and Will Alsop.
A spokesperson for Railtrack said a winner would be selected in July. Railtrack launched the competition in February, when it wrote to 40 international architects inviting them to bid for the scheme.
The masterplan would not be implemented until after the completion of London Underground's East London Line extension, which is routed through Bishopsgate. This is not expected until 2006 or 2007.
Not-for-profit developer the Environment Trust is working with architect HTA to develop an alternative community-led plan for the eastern part of the site.
The trust is running a two-day conference to discuss the future of the site with local groups on 6-7 July.
John Aldenton, the trust's development officer, said the conclusions of the conference would be used as the basis for negotiation with Railtrack.
Aldenton said: "We have got Bengali and local interest groups coming. We are going to come up with something that works."