The Wollongong office of Telstra's Sensis division has been earmarked for closure with the loss of 10 jobs, according to the Community and Public Sector Union.
A union spokesman said the expected closure of the office in the Telstra building on Crown Street - to occur as early as next month - would mean the loss of 10 sales jobs.
The action is part of a broader move by Telstra to cut 800 jobs across Australia.
As well as Wollongong, Sensis offices in areas such as Darwin, Cairns, Townsville, Geelong and Penrith are also under threat.
Sensis managing director John Allan said consultations would begin on proposed changes to its operations and workforce to support its transition to becoming a digital business. Sensis produces the white pages and yellow pages telephone directories.
The job losses will come in advertising operations, sales, management and support areas.
Mr Allan said the changes were necessary in order to support growth in its digital business and respond to heightened competition from rival online and mobile search directories.
"As a leader in digital marketing services and print directories serving Australian businesses, Sensis needs to remain responsive to the changing media landscape," Mr Allan said.
"While these decisions are difficult, they are necessary to ensure Sensis maintains its competitive position."
Union national president Michael Tull said the job cuts would harm regional economies.
"Telstra's actions are sending shockwaves through communities that are already seeing jobs disappearing at an alarming rate," Mr Tull said.
The union believed Sensis had shed almost half of its workforce in the past 12 months, with at least 600 roles sent offshore.
Mr Tull said the cuts come as Telstra's Sensis division delivered a net profit of nearly $600 million.
South Coast Labour Council secretary Arthur Rorris said the cuts were not due to the need for Sensis to remain competitive.
"One thing that we need to be clear about and that is it's a myth that this is about Australian workers being uncompetitive and pricing themselves out of the market," Mr Rorris said.
"Nothing could be further from the truth in this case.
"We understand that the company has made half a billion in net profit and it has nevertheless proceeded to offshore many of these jobs.
"It boils down to this: let's not confuse competitiveness and the need for industries to survive with corporate greed."