The company building the National Broadband Network says a $640 million figure for the cost of repairing and replacing parts of the copper network purchased from Telstra has not been endorsed by its executive.
A spokesman for the company says any costs related to the rollout of the fibre-to-the-node network were accounted for in the corporate plan released in August, which included the increase in peak funding.
The company, however, refused to confirm a report in The Australian newspaper that another confidential document showed it was facing a ten-fold blowout on the original estimation of the network repair costs.
"Your questions relate to a draft document from March (which) has not been endorsed by the executive," an NBN spokesman told AAP on Thursday.
"Risks and mitigation plans for the network are outlined in the corporate plan, and the revised peak funding figure takes these scenarios into account."
In its 2016 corporate plan, the NBN noted the "quality" of the copper network was not fully known as there had been limited opportunity to evaluate the physical infrastructure at significant scale.
"However, it is known that there is significant work required to remove broadband blockers from the copper network," it said.
It goes on to say: "If copper rehabilitation costs are prohibitively high in an area, NBN can choose alternative technologies to reduce costs."
The leaked documents referred to in The Australian reportedly show the NBN expects to spend $26,115 per node to fix Telstra's copper lines to ensure the service quality promised under the coalition's broadband plan is provided.
Assumptions in a 2013 strategic review, prepared after the coalition won power, had put the cost of repairing copper connections at just $2685 for each node, The Australian reported.
Labor's communications spokesman Jason Clare said Malcolm Turnbull had made a mess of the National Broadband Network as communications minister and now prime minister.
"He's doubled the cost, doubled the time it will take to build it and now we find out the cost of upgrading the copper has blown out by almost 900 per cent," he told reporters in Canberra on Thursday.
