Moderate Liberals have unleashed a full court press against a rebellion by Queensland Nationals, declaring the Morrison government must not be in the business of building coal-fired power stations when the market declines to do so.

The firm pushback by Liberals comes as the former Nationals leader Barnaby Joyce is escalating his public interventions, shirtfronting the prime minister late on Monday, declaring support for coal was National party policy, and the government should not “go silent or mute on issues we support”.

With the renewed coal fight opening divisions both within the Nationals, and within the Coalition partnership, Liberals Trent Zimmerman, Tim Wilson and Trevor Evans told Guardian Australia that Morrison was correct to dismiss calls by the Nationals for a new taxpayer-backed coal plant as a “hypothetical debate”.

Their sharp interventions on Monday are indicative of the anxiety many Liberals have that inaction on climate change could cost the Coalition the coming federal election, with the MPs believing it is now necessary to draw a line.

Zimmerman said he was a strong supporter of the government’s recent commitments on Snowy 2.0 and the Tasmanian “battery to the nation” project but he was emphatic in his opposition to government-backed coal.

The Sydney Liberal said “a Liberal government should not be in the business of building new coal-fired power stations in circumstances when the market is not prepared to do so”.

Wilson concurred and said Morrison was correct to hose down the new campaign from the Nationals. “I presume the intention is to deliver lower power prices,” the Victorian Liberal said Monday. “When has government building anything led to lower prices?

“We have a policy, and what we need is discipline so we can deliver our reliable, affordable and environmentally sustainability plan before and after the election.”

Evans, a Brisbane-based Liberal moderate, also distanced himself from the pro-coal campaign from Queensland Nationals, declaring the group a “lonely minority” that is “whistling Dixie on this”.

Evans was emphatic that the current party room would not sign off on taxpayer backing for new coal-fired power when the economics of the development did not stack up.

With the issue erupting into an open power struggle within the government, some Nationals also remain on the warpath. Joyce insisted late on Monday the government should not back off from supporting new coal just because the Queensland government would not approve a new power station – which was the rationale the prime minister offered to reporters on Monday morning.

Joyce told Sky News it was time to double down on supporting coal communities in Queensland, and arguments like the one Morrison advanced should be left to the Labor party. “It is National party policy to support coal-fired power … and you have to stand behind our policy,” the former deputy prime minister declared.

Queensland National Keith Pitt – while trying to hose down Joyce’s positioning against the current deputy prime minister, Michael McCormack, which is an element of the current sortie – also argued north Queensland would have a need for a new high-efficiency coal plant if it was to maintain heavy industry, like smelters, and “you can’t run a smelter on wind and solar”.

The dispute was first triggered last week when an insurgent group of Queensland Nationals MPs demanded McCormack muscle up to the Liberals on power generation, a politically difficult demand for the government, which is trying to bolster its credibility on tackling climate change for fear of losing support in inner-city liberal constituencies in Sydney and Melbourne.

The coal push against McCormack is not only a policy fight but also a power struggle, with Joyce positioning to return to his old job, and some Nationals fretful that McCormack isn’t cutting through with the public.

Morrison raised eyebrows within National party ranks on Monday when he declared there would be “no change” to the Nationals’ leadership despite the current positioning – an observation some Nationals regard as an unnecessary provocation, given the Liberals do not have a vote in the Nationals’ party room.

McCormack has attempted to hold the line on new coal development, saying he is not opposed to new plants, but the business case for any new development has to stack up.

While the epicentre of the coal push is in Queensland, the Nationals’ two most senior party executives hold roles at firms representing energy companies who are pushing for taxpayer underwriting of new coal plants through a program developed by the energy minister, Angus Taylor.

The Nationals’ federal president and vice-president, Larry Anthony and Katrina Hodgkinson, hold senior roles with the SAS Group and Barton Deakin respectively, firms that lobby government as part of their broader business.

SAS Group represents the businesses of power baron Trevor St Baker, who has put in a bid for government underwriting, while Barton Deakin provides services to NuCoal.

Earlier this year, St Baker proposed a $6bn plan for two new coal power plants in New South Wales and Victoria and a pumped hydro facility in South Australia, backed by a Chinese joint venture.

The SAS Group managing director, Peter Costantini, denied any suggestion of a conflict between Anthony’s roles. Anthony does not lobby government for the SAS Group, including for any of St Baker’s businesses, Costantini said.

It was also wrong to characterise SAS Group simply as a lobbying firm, he said.

“A minority of our staff undertake lobbying work,” Costantini said. “Larry is not one of them, and he does not perform work for the firm in question.

“We note that the firm is part of a stable of energy businesses, that includes extensive renewable energy interests and is taking a lead role in advocacy for renewables and emissions reduction.”

Anthony also denied ever having lobbied Nationals members on behalf of resource companies or having any role influencing Nationals policy, Costantini said.

Hodgkinson also denied any conflict of interest in her dual roles. Like Anthony, she said she had no role in lobbying Nationals members on behalf of resources companies, and had not had any role in the Nationals’ policy on coal plants.

Barton Deakin also said NuCoal was seeking advice from them on compensation for expropriated assets.

The lobbyist code of conduct prohibits registered lobbyists from holding senior positions within the party executive. Party executives have powerful roles in pre-selections, campaigning and policy formation. The rule is an attempt to prevent conflicts of interest but it is rarely enforced. Even if it were enforced, there is little serious punishment for breaching the lobbying code.

Guardian Australia is not suggesting Anthony or Hodgkinson are in breach of the code. Neither is a registered lobbyist and both say their work is internal in nature, meaning they do not directly approach government on behalf of private clients.

Hodgkinson has previously told Guardian Australia she took herself off the lobbyist register when she nominated for the Nationals’ vice-presidency.

“I came off all registries upon nominating for the role,” she said in September. “Barton Deakin follows the rules of the code of conduct. The work I do at the company is internal and advisory in nature.”