This is a condition of the government's plan to offer Telstra A$11 billion ($10.7b) for its copper ducts and infrastructure, and have Telstra sign on as an NBN customer.
But the opposition Coalition is attempting to block progress of the legislation until the government submits a detailed cost-benefit analysis of the project, which could cost up to A$43 billion.
The government earlier this week secured the backing of the minority Greens party, in exchange for agreeing to amendments requiring parliamentary approval for an eventual sale of the NBN network assets.
The Coalition today revealed it may yet vote for the legislation, but only if the government agrees to submit to a Productivity Commission cost-benefit inquiry by next May.
Senator Conroy is eager to have the separation bill passed by the end of the senate's sitting session, so that the government and Telstra can meet their proposed deadline of having a deal to take to Telstra shareholders by the middle of next year.
The last scheduled sitting day for the Senate is tomorrow, and the break is likely to last until February.