Optus will compensate more than 8700 users who have been misled on the net speed of the package.
According to the company, it may have violated Australian consumption law (ACL), providing customers with slower speeds than advertising between September 2015 and June 2017.
The Australian Fair Competition and Consumer Council (ACCC) said the slower speed of the network was due to "technical constraints" on consumers' fiber-to-node (FTTN) or fiber-to-building (FTTB) NBN connections.
The maximum download speed of the Boost Max "Optus the highest-priced package" should have been 100 megabytes per second and the maximum upload speed should have been 40 megabytes per second.
ACCC revealed that nearly half of the customers who bought FTTN package couldn't reach that speed.
In addition ,21 per cent of users (2,337 bits) did not even reach half of the above network speed.
"Worryingly, Optus many affected FTTN users don't even have access to the highest speeds for cheaper packages ," said ACCC chairman Simms (Rod Sims).
"We have seen this worrying trend across the industry and we are working to address it. "
More than a quarter of FTTN users (1,519 bits) did not get the highest speed for Optus second-fast packages (50 megabytes per second maximum download and 20 megabytes per second maximum upload).
The number of Optus affected customers, however, is "insignificant" compared to the Australian Telecommunications (Telstra).
"As for telecommunications companies selling products to customers that do not reach the speed of the network, we have taken action, Optus is the second major network supplier we are hitting ," Sims said.
At the beginning of November, ANT admitted that its 42,000 users were getting a slower-than-expected network speed, almost five times Optus.
Optus have informed the ACCC of the court enforcement order detailing the remedies it will take against the affected client.
These remedies include refunds, changes to the net rate package, discounts and allowing customers to withdraw without paying liquidated damages.
Optus were also asked to check with the customer and contact them within four weeks to discuss NBN replacement of the new package to see if they received the promotional network speed.
If the customer's speed is lower than the publicity speed during the inspection, the telecom company will need to inform them and provide remedial measures.
ACCC, however, warned that if customers quit their Optus contract and switch to another network supplier, they might not get faster either.
Optus will contact the affected customer by email or letter by 2 March.
