Labor shadow communications minister Michelle Rowland has questioned the timing of the NBN Co's announcement about delaying HFC connections to the national broadband network, revealing a timeline that shows problems were first identified two years ago.

In a statement, Rowland said leaked documents had identified noise ingress as causing interference and degradation in end-user speeds back in November 2015.

NBN Co made its announcement on 27 November, saying that households and businesses would have to wait between six and nine months longer for connections while the company fixed technical issues affecting the speed that the network can deliver.

Rowland said that the same month (November 2015), leaked documents had indicated that the NBN Co would have to drop the proposed use of the Optus cable network.

"What triggered the sudden sequence of events in November 2017, given the issue was identified over two years ago?" she asked. "Was it the fear of leaks exposing the situation?"

Michelle Rowland: "why has the HFC delay announcement been made now?"

The NBN Co has said that applications from residents who are within the HFC footprint will not be entertained after December 11.

"Was it the fear of the pending ACCC speed monitoring programme focusing on HFC as the first technology off the rank?" Rowland asked. "Were dropouts on the HFC network reaching a state of no return? Or was it a combination of all-the-above?"

She had a dig at Prime Minister Malcolm Turnbull, who was communications minister when the Coalition came to office in 2013 and decided to change the technology mix for the NBN.

"For all of Malcolm Turnbull’s platitudes about making the NBN more transparent, his latest debacle on HFC shows it has never been more opaque," Rowland claimed.

A timeline of events that ended in the HFC delay, as outlined by Rowland:

November 2015 – leaked documents identify noise ingress on HFC as the cause of interference and degradation in end-user speeds.

November 2015 – leaked documents indicate NBN will abandon the Optus HFC network.

February 2016 – NBN chief executive denies company will abandon use of Optus HFC infrastructure.

September 2016 – NBN abandons use of Optus HFC infrastructure.

14 November 2017 – The Senate votes to order a committee hearing with NBN executives scheduled for 23 November.

22 November 2017 – NBN writes to (communications) minister (Mitch Fifield)to advise they are seeking to halt the HFC rollout.

23 November 2017 – Chief NBN engineer questioned on HFC interference, but no mention of the pending rollout halt at the Senate hearing.

27 November 2017 – NBN announces a halt to the HFC rollout.