Telstra has paid $2.5m in fines for failing to list close to 50,000 people as private numbers to prevent them being listed in public phone directories.
When telecommunications companies register new phone numbers with customer information, they are required to specify whether the phone number should be listed or unlisted.
The authority also found Telstra failed to provide or update the data on the national database for customers of its subsidiary internet service provider, Belong, on 65,000 occasions.
The failure to register unlisted numbers could also lead to harm, she said.
It is the second time Telstra has been found in breach of the obligations, with the first finding in 2019 after Telstra self-reported it to the authority.
Acma said the $2.53m penalty was the largest of its kind to be issued for such a breach.
