The federal government has blocked modelling for its net-zero emissions plan from being released publicly, despite a Senate order for it to be shared last week.

Despite the Nationals trumpeting having reached an agreement with the Liberals on the plan, still no details of the strategy have been released, with politicians and federal department officials refusing to answer questions at Senate estimates hearings on Monday.

“The first rule of Fight Club is not to talk about Fight Club,” Nationals minister Bridget McKenzie said, as she dodged questions on what concessions the junior Coalition partner had extracted from Prime Minister Scott Morrison for their support.

Labor senator Penny Wong claimed the government had an “addiction to secrecy”, blasting the repeated non-answers across multiple Senate estimates hearings. Labor’s shadow climate minister, Chris Bowen, called it an “outrage”.

Nationals leader Barnaby Joyce finally confirmed late on Sunday that his party had reached an in-principle majority agreement on Australia aiming for net-zero emissions by 2050. However, Mr Joyce would not confirm whether he personally backed the target, and it has been reported that he spoke against the plan in the Nationals’ party room.

Mr Morrison is set to officially sign up to the pledge at the Glasgow COP26 climate summit at the end of this week. But few details of the plan – such as its cost, how many jobs it will create or threaten, and which policies it will use – have so far been shared.

Barnaby Joyce said “I don’t have to” say what’s in the net zero agreement. Photo: AAP

Mr Joyce said the Nationals had negotiated to include “conditions that were never there before”, claiming regions would fare “vastly better” following the party’s intervention.

But in morning media appearances, Nationals MPs refused to say what they had asked for or received.

Senator McKenzie, appearing before a hearing of the Senate’s regional and rural affairs committee, said she could not speak about the net-zero plan as it was to be debated by federal cabinet.

“That is a matter for cabinet, I’ve got nothing more to say,” she said, under questioning from Labor’s Murray Watt.

“I’m not suggesting anything to you about what may or may not be in a cabinet submission, because that would actually be not the right thing to do.”

Senator Watt asked if the Nationals had demanded a new coal-fired power station. Senator McKenzie answered with a reference to the movie Fight Club, about a secretive underground boxing group for men.

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In other hearings on Monday, government ministers and department officials also declined to share details of the plan.

International Development Minister Zed Seselja, representing Energy Minister Angus Taylor in an environment committee hearing, revealed that the government had made a “public interest immunity claim” on the economic modelling that underpins the plan.

Mr Taylor said that, because the modelling informed or was the subject of cabinet deliberations, it couldn’t be released – despite the Senate order, and Senator Seselja himself promising a “more detailed response” this week.

“There is a long standing principle that documents for consideration of cabinet remain confidential,” Senator Seselja said.

The Senate ordered that this modelling be released last week, but Senator Seselja said that due to the “sensitivities” of it being a cabinet document, it would be released this Friday. But now, the document will be blocked from release, following the immunity claim.

One Liberal member described the immunity claim on the modelling as “bulls–t” to The New Daily.

Nationals senator Matt Canavan was also critical of the modelling remaining “secret”. He told the Nine Network that the net-zero plan would “end in tears”.

At a press conference, Mr Bowen blasted the secrecy.

“They’re making it up as they go and they’re refusing to tell the truth,” he said.

“This mob who campaigned day after day at the last election, about the cost of climate action, now saying the Australian people do not have a right to see their modelling. It is an outrage.”

Back in estimates, Senator Seselja also declined to answer questions on the Nationals’ negotiations.

“What you’re asking for is for this committee to be able to effectively interrogate the internal deliberations of cabinet and that has not been the approach in the past,” he said.

Penny Wong claimed the government was “addicted to secrecy”. Photo: AAP

The environment committee was suspended for about 15 minutes after Labor senators protested that department officials declined to answer questions on the net-zero plan.

Industry department boss David Fredericks would not say if the department provided advice about concessions demanded by the Nationals in exchange for a net-zero target.

“If you’re asking about a document which is a political document passing between the National Party and the Prime Minister, then I can’t comment in on it,” he said.

But in the afternoon, one of the Nationals’ demands was revealed. Nationals MP and Resources Minister Keith Pitt was re-instated to cabinet, boosting the rural party’s representation from four members to five, by Mr Morrison.

Mr Pitt’s abrupt reinstatement seems part of the Nationals’ price for support. Mr Morrison said in a statement that Mr Pitt would work with Mr Taylor “to ensure we reach our emissions reduction targets through technology that will empower our industries and regional communities”.

Mr Morrison flies to Glasgow on Thursday for the United Nations climate summit. The net-zero plan will be discussed and likely endorsed at a cabinet meeting on Monday, with further details expected to be released later this week.