The city council has been urged to investigate after tenants said their landlord offered them a rent reduction in return for supporting a controversial planning application.
Jamie Osborn, a city councillor, has asked officials to look into plans to build penthouses on the top of Vantage House, in the city centre, to check that no rules have been broken.
Mr Osborn - whose Mancroft ward covers the site - has handed them a letter, which was sent by Avivco Developments to people already living in the block, saying those who backed the scheme "will benefit from a fair rent reduction".
Mr Osborn said: "I have passed Avivco's letter to tenants on to the relevant authorities and asked them to investigate the letter.
"It is vital that residents are able to express their views on planning applications freely and without undue influence, and that the planning system is fair and transparent."
In response, the company said: "The reduction was to cover noise and disruption during construction."
But Avivco has not responded to further questions about whether the wording of the letter - which appeared to make the rent reduction conditional on support for the planning application - was an error.
The company wants to build four penthouses on top of the building at the junction of Pottergate and Fishers Lane.
Its application was originally withdrawn last year after tenants and councillors submitted objections.
But the developer has now submitted a revised application.
In the letter to tenants - which has been seen by the newspaper - the firm writes: "We need your support so we can deliver its benefits to our tenants.
"Therefore, we kindly ask that you comment positively about the application and send a letter of support for the scheme. Please include your name and apartment number.
"Tenants that support the scheme will benefit from a fair rent reduction for a reasonable period of time."
Architect Jon Boon, whose company has drawn up plans for the rooftop apartments, said he was surprised by the wording of the document.
"I knew they were going to offer a rent reduction to compensate for any noise or disturbance during the construction process which would be a reasonable offer," he said.
"But it seems like that has been slightly twisted one way or another."
There are currently 28 public comments on the Norwich City Council planning portal giving a response to the application - with 26 objections and two supporting.
Among the complaints are claims about the current conditions at Vantage House, with comments about its "unfinished windows", "only one working lift", "unsafe car park which has had potholes" and "a mountain of rubbish piling up at the few skips".
Others have raised concerns that the penthouses will be a potential "eyesore", and will have a negative impact on the city skyline.
Mr Boon added: "It's a tricky design. There are plenty of points of view that it's a conservation area but what we will do will it make it less unattractive in its form."
Mr Osborn, a Green Party councillor who also sits on the county council, said: "I had previously raised concerns about the conversion of offices in Vantage House into the poor quality and cramped flats, seemingly prioritising developers' profits over decent housing.
"I have also raised concerns about Avivco's new planning application to put penthouses on top.
"The plans would make an already ugly building even uglier, spoiling the historic Pottergate and St Giles streetscape, while failing to provide decent quality housing."
In their new application, the developers say "the form and aesthetics of the proposal has been carefully considered to respond sensitively to the surrounding context".
They go on to say the scheme will create "sustainable family homes" to "transform the building into "an asset that positively contributes to the conservation and character areas".
Malcolm Green, 61, who lives near Vantage House, is among the objectors.
"You can't imagine another two storeys on top of it," he said. "They should knock the whole building down."
The building originally housed offices. It was converted into 44 apartments after Norwich City Council granted permission in August 2020.
Norwich City Council has said it will not comment on the case raised by Mr Osborn.
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