Jersey's Housing Minister says he'll try and block the sale of St Helier House to a private developer.
Senator Sam Mézec is urging parishioners to oppose the £2.9 million deal.
St Helier ratepayers will be asked tomorrow evening to agree to the sale of the former residential home and Westmount Day Nursery opposite People's Park.
Town Hall officials are recommending parishioners accept an offer from an unnamed bidder.
Senator Mézec says he is deeply concerned that a deal could be done without any information about who is buying the high-rise and what their plans are - other than to 'refurbish it into 'residential accommodation'.
The details have been withheld for commercial reasons.
In a social media post the Minister says he is worried there are no guarantees the purchaser won't overdevelop the site.
"We cannot be sure that the purchaser will not be cramming as many tiny flats as possible onto the site to sell on at extortionate rates, potentially not even to owner occupiers, but to foreign buy-to-let or lock-up-and-leave investors.
At a time where rent inflation is high and affordable homes waiting lists are getting longer, I do not believe that a public authority should be potentially contributing to the problem by selling off a site like this without guarantees that the development will actually meet the housing needs of ordinary Islanders."
Senator Mézec says he will be attending the Parish Assembly, which starts at 7pm on Wednesday at the Town Hall, to vote against the proposal. He is urging other St Helier residents to do the same.
He says that if the proposition is lost he will do what he can to work with the Constable and the parish authorities to find an option that provides 'appropriate guarantees' and 'not just generate a profit for a private developer'.