The NBN Co says it now expects there to be more than 100,000 fewer homes connected than originally forecast this year.

The company revised down its target from 341,000 properties connected by the end of June to between 190,000 and 220,000.

NBN Co chief executive Mike Quigley said he was disappointed by the delay but it would not have an impact on the 2021 completion date.

Mr Quigley said contractors caused the delay.

"This is not about labour rates, it's not about labour shortages... there are enough workers in Australia to build this network," he said.

"It's about our contractors putting the right people in the right place at the right time."

He said more specialist workers will be trained for the project.

"The problem is we are just not seeing the ramp up of construction workers on the ground that would be needed to deliver these targets," he said.

News of the revised figures came as much of the media's focus was centred on Canberra and the Labor leadership crisis.

Mr Quigley said he was not using the leadership spill as cover for the downgrade.

"We had a board meeting scheduled today and the board meeting took place, the board had to oversight and approve the reforecasting," he said.

"It's a major event."

But Opposition communications spokesman Malcolm Turnbull took to Twitter to express his scepticism about the timing of the announcement.

NBN takes out the garbage under cover of Labor leadership drama shar.es/eEPvY via @sharethis — Malcolm Turnbull (@TurnbullMalcolm) March 21, 2013

The revelation comes after the rollout in the Northern Territory was hit by another delay yesterday when building contractor Syntheo pulled out.

Syntheo had been contracted by Service Stream, who was in turn employed by the NBN Co to deliver connections to the Territory, Western Australia and South Australia.

The NBN Co said it would employ its own contractors to lay the fibre.

But Communications Minister Stephen Conroy had a positive take on the withdrawal, saying it would benefit other states.

"This will enable the NBN Co to take direct control of the rollout in the Northern Territory, allowing Syntheo to concentrate its resources on the rollout in Western Australia and South Australia, bringing high-speed broadband to Australians in these states sooner," he said.

Meanwhile, the NBN Co today announced Siobhan McKenna was taking over from retiring chairman Harrison Young.

Mr Young had been chairman for three years.