TPG has been fined $360,000 by the Australian Communications and Media Authority for not unsubscribing customers who requested to stop receiving marketing messages.
ACMA investigated complaints against TPG and found that during April this year, the internet provider's systems were not properly processing unsubscribe requests.
Consumers complained to the authority that despite having requested not to receive any further marketing communications, TPG continued to send short message service (SMS) text messages to them.
Under Australia's Spam Act 2003 law, consumers must give their consent to receive commercial electronic messages.
ACMA said TPG had breached the Spam Act 2003 by not respecting consumer requests to opt out of receiving marketing material.
The authority said it decided against taking TPG to court as the provider had co-operated with ACMA, admitted the breaches, and took steps to remedy the cause.