Big staff reductions have prompted Telecom to leave one of its four buildings at its Victoria St headquarters in Auckland.
Jim Robb of Telecom property projects said the business no longer needed four towers in the campus-style property.
"You will no doubt be aware that there has been staffing realignment at Telecom," Robb said.
"We are now in the position where we can operate from three of the four towers so Telecom's about to advertise one complete tower of about 6,500sqm for sublease or assignment."
Telecom is shedding between 930 and 1,230 staff.
The four towers were developed by Manson TCLM, then leased to Telecom on a long-term basis.
The buildings' later sale to a syndicate of buyers was said to be the biggest commercial property deal of 2012, at around $280 million.
In late 2011, Telecom shifted about 2,650 staff to the four-building campus from various properties around the city.