Hundreds of thousands of Australians could be forced to wait months longer than expected to be connected to the national broadband network via pay television cables.
NBN Co on Monday announced it was temporarily suspending the rollout of the hybrid coaxial-fibre (HFC) network to "improve customer experience".
It warned of delays of six to nine months.
"While the good news is that we are working on a better experience for the internet providers and end users, the improvement efforts will take additional time," CEO Bill Morrow said in a statement.
"We remain confident of reaching our goal of completing the build and connecting eight million Australian premises by 2020."
Nearly three million premises are slated to get the NBN via HFC.
Almost one million are ready to connect via HFC, with 370,000 having already done so.
Mr Morrow said too many Australians weren't having the experience they deserved when getting connected over the HFC network and some weren't experiencing its full potential.
Internet providers have been told of the changes, and the NBN website will be updated in coming weeks so people can check their address to see if there are any changes to their connection date.
Labor's communications spokeswoman Michelle Rowland said Malcolm Turnbull used to champion the "dud" technology.
"This was supposed to be the game-changing technology," she told reporters in Canberra.
"This was supposed to be future-proofing technology that would save four years and $30 billion by switching to the multi-technology mix. It has utterly failed."
Telstra will assess the impact of the delay on its outlook for 2018.
"Telstra will keep impacted customers informed and discuss disconnection obligations with NBN Co and the Australian Consumer and Competition Commission to minimise customer impact during this period," it said in a statement to the Australian Securities Exchange,
