The union representing Telstra field staff estimates up to 80 per cent of the telco's "disgraceful" copper-wire network pits have been patched together by plastic bags or ring-barked cables.
It's the very same copper network NBN Co plans to buy or lease off Telstra for the fibre-to-the-node national broadband network (NBN) being championed by the Abbott government.
"This would be a fraud on the Australian taxpayer," CEPU NSW assistant secretary Shane Murphy told a Senate hearing on the NBN in Canberra on Thursday.
Mr Murphy said 75 to 80 per cent of Telstra's copper pits were as rotten as the pictures he brought to the Senate committee, which showed the ageing network being crudely held together by ring-barked cables and covered by plastic bags in a vain attempt to keep water out.
"This is the exact network that will be sitting outside there, tying into the NBN that is built to the node," he said.
Mr Murphy said the network was in reasonably good condition when Telstra was privatised in the late 1990s.
However, proper maintenance of the network's copper pits had since disappeared.
"Telstra has been consistently pushing workers to simply get the customer services up and running, band-aiding the network, and moving the employee or contractor quickly onto the next job," he said.
Telstra would have no idea just how bad things were in the copper pits, Mr Murphy added.
"Workers and contractors are now so frustrated with what they're working in, and without being given the adequate responsibility to be able to fix it appropriately, they're not reporting them."
Mr Murphy said the communications union is about to begin a campaign in a number of electoral seats around the country to highlight the issue.
Earlier on Thursday, the Senate select committees summonsed NBN Co chief Ziggy Switkowski to front a parliamentary inquiry.
Dr Switkowski and other senior NBN executives have said they are reluctant to appear before the committee in person.
The committee has issued a summons requiring their presence at an inquiry hearing in Canberra on Friday.
Committee chair Kate Lundy said on Thursday the summons had been issued with regret, given the government's public commitment to openness and transparency in matters relating to the NBN.
The Senate has asked the committee to inquire into the government's reviews of the NBN and the governance of NBN Co.