Residents living near to one of Northampton's best-known hotels are demanding its 18-bed extension is dismantled.
The owners of Westone Manor Hotel in Fir Tree Walk were given permission to extend the north wing of the former stately home by another floor in 2017.
The building work, a 20-metre metallic was completed late last year.
But more than 150 nearby residents have now signed a petition because they say the extension does not resemble the approved plans - and appears to be two storeys in height.
Northampton Borough Council has now made the hotel owners apply for retrospective planning permission.
"They just carried on building," said retired electrician Dave Peck, 68, who gathered the petition names in just one day.
"There were complaints from residents all over here because it wasn't in compliance with planning."
The additional floor to the north wing appears to have a second row of windows, giving the building the impression that, in fact, two storeys have been built on top of the old part of the building.
The metallic design, the residents argue is out of keeping with the area.
"With complete disregard for the original plans submitted, building work was undertaken and completed" reads the text in the residents' petition.
"The result was two-storey frontage and a slanting, corrugated roof, creating an ugly, industrial-styled eyesore."
Mr Peck gathered the names on the petition from just three streets, Ashley Way, Fir tree Walk and Moorland Close.
Although the work has been completed, if the council turns down the retrospective planning application, it could order the building to be dismantled.
But owner of the premises, Harry Sookun, said the retrospective planning application currently being decided by council officers is simply a formality.
He said: "There has been a perception in the community that the extension should have been built with a flat roof.
"The set of plans which was validated and approved clearly shows the height of the front elevation facing Fir tree Walk to be 11 meters and 8.7 meters at the rear facing Ashley Way."