Three broadband internet providers have been fined $33.5 million after failing to ensure some customers could achieve internet speeds they were paying for.
Telstra will pay $15m after action was taken by consumer watchdog, the ACCC in the Federal Court.
The penalty was agreed between Telstra and the watchdog, and approved by Justice Mark Moshinsky on Friday.
Optus agreed to pay $13.5m while TPG will pay $5m.
Each of the three providers admitted liability for contraventions of the Australian Consumer Law, Justice Moshinsky said.
Three separate cases were brought by the Australian Competition and Consumer Commission over representations made to residential customers about broadband internet services using the NBN.
The judge said each of the representations differed, but broadly involved customers being told their maximum attainable speeds would be tested within a reasonable time.
In a majority of cases that occurred, but some customers did not have speeds tested and ended up subscribing to a plan for speeds they couldn't achieve.
Customers weren't notified or given the option to move to a different plan, Justice Moshinsky said.
Affected customers have already been contacted by the companies to arrange refunds, the ACCC revealed.
"Some customers may have paid for a 50 or 100 Mbps plan believing their NBN connection could support the higher download speeds, even though they would have been better off paying for a lower speed plan," commissioner Liza Carver said.
"It is illegal for businesses to make false or misleading representations to consumers about the performance characteristics, nature, standard or quality of products and services."
TPG was ordered to implement a consumer law compliance program, while Optus must update its existing program.
Telstra has been under compliance obligations since 2020 when the ACCC took action for unconscionable conduct toward Indigenous customers.
Justice Moshinsky's reasons for the orders will be handed down at a later date.