Optus has agreed to compensate over 8,700 customers that it misled about the speed of their plans.

The telco admits it is likely to have breached the Australian Consumer Law (ACL) by providing slower-than-advertised speeds between September 2015 and June 2017.

The ACCC says the slower speeds were due to “technical limitations” on the customers' fibre to the node (FTTN) or fibre to the building (FTTB) NBN connections.

Optus’ top-tier “Boost Max” claimed to provide maximum download speeds of up to 100 Mbps and upload speeds of up to 40 Mbps.

But the ACCC says almost half the FTTN customers on that plan (5,430 people) could not reach such speeds, while 21 per cent of customers (2,337) could not get even half that speed.

“Worryingly, many affected Optus FTTN customers could not even receive the maximum speed of a lower-tier plan,” ACCC chairman Rod Sims said.

“This is a concerning trend we have seen throughout the industry and we are working to fix this.”

More than a quarter of customers on Optus’ next fastest plan (50/20 Mbps) could not receive the stated top speed.

Optus’ court-enforcable undertaking is low compared to that of industry leader Telstra, which recently agreed to compensate 42,000 of its customers for slower-than-expected speeds.