Victoria is continuing to express “major” concerns about the federal government’s national energy guarantee before make-or-break discussions on the proposal in August.

The state’s energy minister Lily D’Ambrosio argues it would be a leap of faith to sign up when the Coalition party room is yet to formally tick off on the emissions reduction component of the Neg, and when federal government MPs are acting like “coal ideologues”.

D’Ambrosio will face questions about Victoria’s position on the Turnbull government’s policy when she attends a clean energy conference in Sydney on Tuesday with other key players, including the federal energy minister Josh Frydenberg, and senior officials.

In an effort to keep his state counterparts at the table, Frydenberg has offered a two step process before sign-off which will include showing them the federal legislation giving effect to the emissions reduction components of the scheme on 14 August, after the package clears the Coalition party room earlier in the day.

D’Ambrosio will say on Tuesday a national approach is required to settle energy policy and the state is cooperating in good faith, “but it’s no secret that like many other states, we have major concerns about [the Neg]”.

The Labor states have been concerned the government might provide subsidies to prolong the life of coal plants as part of a quid pro quo to stop its own MPs from crossing the floor once the legislation gets to federal parliament.

They have also signalled they want the scheme to be made easier to adjust to a higher emissions reduction target rather than with low ambition locked in for a decade.

“Malcolm Turnbull is trying to get us to sign up to something that hasn’t gone to his own party room – a place full of climate sceptics,” the Victorian minister will say according to a speech extract circulated before Tuesday’s conference.

“Every time we get close to a national energy policy, the Coalition party room shoots it down. How can we have any confidence in what they’re asking from us if it hasn’t been through his party room first?”

We need proper engagement, not just a half-baked report thrown over the fence.

Guardian Australia understands the Victorian government – which faces a tough state election contest later this year – has been pushing behind the scenes to delay a final decision on the Neg until later in 2018, but that is being resisted by both the federal minister and energy bureaucrats.

Victoria and Queensland are under pressure from the environment movement, some elements of the solar industry and the activist group GetUp! to torpedo the scheme unless it contains an emissions reduction target more ambitious than a 26% cut on 2005 levels by 2030.

Another flashpoint behind the scenes is the states and territories have not yet been given access to the modelling used to help craft the final cut of the policy.

It is understood the modelling will be handed to the states and territories on Tuesday in another attempt to remove roadblocks to an agreement at the first meeting of the Coag energy council on 10 August.

Stakeholder pressure is increasing on Victoria and Queensland to veto the scheme if all the relevant detail is not in the public domain in good time for that meeting. Any one of the states or territories can kill the scheme.

A new letter signed by 22 respected energy researchers calls on the states to ensure they have access to the full modelling, including all assumptions that have a bearing on the assessment of power price reductions under the scheme, before they sign on, so the material can be peer-reviewed.

One of the group of researchers, Simon Holmes à Court, a senior advisor to the climate and energy college at the University of Melbourne, and the founding chair of Hepburn Wind, said there needed to be “proper engagement, not just a half-baked report thrown over the fence”.

He said the material the Energy Security Board released last week in its final design paper did not line up with an authoritative long-term forecast from the Australian Energy Market Operator – the integrated system plan – and experts had been unable to reconcile the differences.

“The Neg mechanism itself is unstudied,” Holmes à Court said. “It is poorly understood and there is no evidence that it has been rigorously modelled.

“The Aemo forecast was a nine month exercise, a huge rigorous thing that we can trust doesn’t have any agenda.”

Holmes à Court said there was an enormous amount of pressure being applied to the states to sign on in August when the Neg does not take effect until 2020, and it was unclear what was driving the urgency of a resolution.

If Frydenberg manages to secure a sign off from the states and from his party room colleagues in August, the political battle over the policy will return to the federal parliament. The government will need Labor’s support to legislate the Commonwealth components.

The shadow climate change minister Mark Butler told Sky News on Monday that Labor’s main issue with the Neg was the emissions reduction target, not the mechanism.

Butler was pushed to nominate what emissions reduction target Labor wanted for the scheme given it rejects the Turnbull government’s proposal of a 26% reduction in electricity by 2030 as too low to see Australia meet its Paris commitments.

Butler said Labor’s target would be “at least” 45% – which is Labor’s economy-wide target for emissions reduction – but he suggested the specific number for electricity may need to be set by an independent authority.

He then said if the Neg legislation came before the parliament before the end of 2018, Labor would “prosecute” a 45% target.

Butler said Labor would take a policy framework to the next election setting out requirements for emissions reduction in electricity, in transport, and for “the big polluters ... largely manufacturing, mining and the LNG sector”.