NBN Co has missed its first regulated deadline to produce one-year and three-year construction plans, with no firm date given for their creation.

The admission is contained in letters between NBN Co's head of regulatory affairs, Caroline Lovell, and the ACCC's group general manager for communications, Michael Cosgrave, dated April 2, 2014.

Under the special access undertaking [pdf] approved in December last year, NBN Co is required to publish a three-year construction rollout plan "on or before 31 March of each year".

The company is also required to update a rolling one-year rollout plan on a quarterly basis.

But neither document was given to access seekers by this year's deadline.

Lovell said NBN Co "is fully aware of [its] commitments and has been working hard to met them".

"However, the purpose of this letter is to advise the ACCC that NBN Co is not proposing to provide the three-year and one-year construction rollout plans by 31 March 2014," she wrote [pdf].

"[We] will use [our] best endeavours to complete and provide these plans as soon as possible".

Lovell partially blamed NBN Co's "major change in direction to the multi-technology mix (MTM) architecture as a key reason for the rollout planning delay.

She also said the company had been putting its resources to addressing "planning and construction issues that led to delays and frustration in the past".

NBN Co recently committed more of its field force to reduce numbers of 'held orders' — those with a delayed last mile connection to the NBN — on its books.

Lovell said that had NBN Co pushed out its construction plans on time, they would have been "incomplete or necessarily caveated", and may have sown confusion rather than clarification among access seekers.

Cosgrave said the ACCC noted NBN Co's "claim that there is not a sufficiently robust basis to prepare the plans", and more or less told NBN Co to inform affected ISPs directly.

Access seekers that have issues with the missed deadline are invited to email the ACCC by April 9.