The Labor-Greens majority of the Senate Standing Committee investigating the National Broadband Network (NBN) has been accused by Liberal members of the committee of "bullying" NBN Co executives.

In the second report of the committee (PDF) tabled in parliament on Thursday, the committee said that 18 months into the Coalition government taking over the project, NBN Co could not yet provide certain figures on the progress of the rollout, and that the figures provided were out of date and unreliable.

The report states that the "unreliability" of the strategic review conducted in late 2013 means that NBN Co has been forced to release a new figure for the cost of rolling out fibre to the premises (FttP) at over AU$4,000 per brownfields premises. The committee stated that this figure should not be relied upon.

"Most of the cost increases for FttP evident in the cost per premises review may be attributed to higher rates and dispute claims negotiated by current NBN Co management since September 2013, and changed accounting practices (such as capitalising operational expenditure)," the committee stated.

"AU$4.5 billion in FttP architecture savings signed off by previous management -- attested to by NBN Co personnel as implemented, and borne out by the Melton 10 trial -- also appear to have gone missing in these numbers. The committee considers that the cost per premises review should be treated with caution."

In light of this, the committee has recommended that NBN Co release unredacted versions of the strategic review, the 2014-17 corporate plan, and the 2015-18 corporate plan.

The dissenting report, from Liberal Senators Arthur Sinodinos, Anne Ruston, and Dean Smith, however, slammed the report of their fellow committee members.

"The conduct of the committee has been an abuse of the Senate's power. The behaviour of some committee members has been calculated to bully and intimidate key NBN Co executives, and undermine the NBN's capacity to deliver on its operational targets," the senators stated.

"Since November 2013, the committee has called 22 hearings. NBN executives have been demanded to appear before the committee for a total of 272 hours. By contrast, the Joint NBN Committee of the previous parliament called NBN executives to appear for a combined total of 39 hours through eight hearings."

Former Communications Minister Stephen Conroy -- who arguably has more understanding and knowledge of the project than any other parliamentarian -- has dominated the committee hearings and questions to NBN Co executives. The senators suggested that the committee may be used to "make rhetorical political points which have no basis in reality".

"Assertions that the NBN is missing operational targets, that the NBN has become more secretive rather than less, and that the multi-technology mix will not deliver the benefits to the digital economy are not based in fact."

The senators have again called for the committee to be dissolved and re-established as a joint standing committee as was the case under the former Labor government.

The government has attempted to dissolve the committee on a number of occasions, but has not succeeded so far. Labor and the Greens are resisting re-establishing the joint committee, because it would likely have a majority of Coalition MPs and senators -- unlike the last committee, where Labor did not have a majority and it was chaired by then-Independent MP Rob Oakeshott.