Manchester City Council has issued enforcement notices to the owners of 24 houses on Braemar Road, Brailsford Road and Moseley Road in the popular student area.
Fourteen of the properties are owned by two landlords and relate to "poorly designed first floor rear extensions which have been put up without planning permission". Obeying the proper planning process, the council said, "would have allowed the landlords to come back with more appropriate and acceptable designs."
The landlords have up to nine months to remove the extensions and restore the properties to their original condition. If they fail to do this, the council could take the landlords to court where magistrates could issue fines of up to £20,000 for each property.
The owners can appeal to Communities Secretary Eric Pickles.
Cllr Nigel Murphy, Manchester City Council's executive member for the environment, said: "It's very unusual to have so many unauthorised extensions in such a concentrated area, and this has had a real impact on the appearance of the neighbourhood.
"We encourage investment in properties which improve the look of our neighbourhoods and we ask developers and homeowners to first contact our planning department to discuss any proposed alterations. However, we will always follow this action when developers build extensions that are poorly designed and have a negative impact on a neighbourhood."