Housing campaigners will hold a meeting next week over the future of the Holloway Prison site in Islington.
Peabody Family Voice (PFV), launched last year by tenants of the housing association in Hackney, feel the land should have been kept in public ownership for council homes.
It was sold to Peabody for £81million earlier this year, with Sadiq Khan giving them a £42m loan on the understanding 600 of the 1,000 homes scheduled to be built are "genuinely affordable", with 400 at social rent.
The group said: "There should be a clear commitment from Peabody to consult at every stage and provide detailed plans of the proposals.
"Community groups are concerned Peabody is trying to rush through a planning application without giving local people a proper opportunity to comment, and are keeping the terms of the loan secret."
PFV have also queried why Peabody needed to borrow the cash when it had a surplus of £148m last year.
Speaking at the event will be Nick Wakeling from Plan4Holloway, Claire Cain from Women in Prison and a representative from Peabody.
The event will be held at the Pembury Estate Community Centre in Dalston Lane on Monday at 7pm.
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