An Optus outage that saw triple zero calls fail to connect and linked to two deaths is set to land the telco in court.

The Australian Communications and Media Authority (ACMA) has commenced Federal Court proceedings against Optus Mobile.

An Optus spokesperson acknowledged the filing but said "it would be inappropriate for us to comment on the legal proceedings."

The telco said it "continues to invest in network resilience, strengthen our systems and processes, build and foster a culture of transparency and accountability, and improve the services our customers and communities rely on every day."

The ACMA action relates to a 13-hour outage in September 2025 caused by a firewall upgrade.

The regulator alleges breaches by Optus in its obligation to give customers access to emergency calling services, and in ensuring “those emergency calls were carried to the relevant termination point”.

It alleges this occurred on 1005 “occasions”  and seeks financial penalties against the telco.

ACMA chair Nerida O’Loughlin said in a statement that providing access to the emergency call service “is essential to protecting the Australian public.”

“Giving access to the emergency call service is not optional, it is a fundamental legal obligation and the most important public safety responsibility telecommunications providers have,” O’Loughlin said.

O’Loughlin said that one of the reasons ACMA brought this latest action is because the incident represented a “recurrence of a major network outage affecting emergency calls”.

A previous November 2023 outage - caused by the triggering of a safety preset in Optus’ routers - also impacted triple zero calls, and led to a $12 million penalty being paid.

ACMA said that the maximum penalty in the current case is $250,000 per contravention.

O’Loughlin said the recurrence “so soon after the November 2023 outage is a significant concern and one of the reasons the ACMA has decided to take this matter to court.”