The chairman of the competition watchdog has declined to guarantee it will approve the $11 billion deal between Telstra, NBN Co and the Federal Government before its set expiry date on December 20.
The deal was almost unanimously approved by shareholders at Telstra's annual general meeting on Tuesday, with 99.45 percent in support of the deal.
The approval overcame a significant hurdle to the deal in addition to a favourable ruling from the Australian Tax Office, which Telstra received last month.
However, the structural separation undertaking and accompanying draft migration plan underpinning the deal must also pass approval by the Australian Competition and Consumer Commission (ACCC).
The watchdog has two months to do so, under a deadline set by Telstra and NBN Co as part of the negotiated terms. Without final approval from ACCC, the deals are deemed null and void.
In what ACCC communications manager Michael Cosgrave characterised as a "large number of concerns", the watchdog has pushed for Telstra to provide more information on the undertaking.
Among other elements, the watchdog has looked to more tightly regulate Telstra's wholesale and retail arms during the transition phase to the National Broadband Network.
ACCC chairman Rod Sims said the communications team was working on approving the deal.
"As I understand it, under the current time frame the deal will need to be signed off by December 20, when the deal actually expires," independent senator NIck Xenophon asked of Sims during a Senate estimates hearing on Wednesday night.
"We're working to achieve that objective but I can't guarantee that we will," Sims said.
Cosgrave said any further movement on the deal's approval was "very much in Telstra's hands".
The telco has confirmed it will do so in a matter of weeks but "material" changes in the deal could force a second vote from shareholders to approve its passage.
Chief financial officer John Stanhope would not clarify on Tuesday what the company deemed as material.
Though a second structural undertaking submission would not have to go through the same industry consultation process as the first, Sims could not clarify how long a final approval would take once the company had received the revised undertaking.
"We'll make our assessment on an appropriate basis within the legislative framework we're working in," he said.