Mr Buchanan said the council had obtained legal advice to see if there was a viable case to be answered through the court.
"It's not our preferred outcome but when these things are done in a blatant manner ... you are left with little choice.
"It's part of enforcement, it is expensive and difficult [but] it was a carefully weighed up decision.
"We expect the documents to be lodged late next week or early the following week."
Chief executive Paul Crimp said council had considered its options carefully.
"We are supportive of the development but the rules have to be followed."
Development was still able to continue as Mr Pilbrow had applied for and obtained the required consents for building and the construction of a new building, beside it, from the council.
Mr Pilbrow said he wouldn't like to comment at this stage, until he received official documents from the council but he said the development could be affected.
The former Four Square is expected to house five retail outlets and a cafe, and the new building to house two retail shops, a restaurant and offices.
The district plan rule aims to protect the town's historical character.