Nationals minister Bridget McKenzie has declared “it will be ugly” if the prime minister, Scott Morrison, commits Australia to a net zero emissions target by 2050 without the formal imprimatur of the Nationals party room.

McKenzie’s assertive warning shot at Morrison on Wednesday came as the mining giant Rio Tinto became the latest resources player to unveil a new target to reduce direct and indirect emissions by 50% by 2030 – tripling the company’s previous commitment.

Rio’s more ambitious medium-term target follows the Nationals vetoing an effort by Morrison to increase Australia’s 2030 target beyond the current 26-28% reduction. The mining behemoth says its more ambitious pledge will be backed by $7.5bn of “direct investments to lower emissions between 2022 and 2030”.

With the Cop26 climate talks in Glasgow looming, the prime minister is attempting to land a net zero commitment before he departs Canberra next Thursday for the United Nations-led conference.

McKenzie, a cabinet minister, has not been clear about whether she is prepared to support that 2050 target. But while she fired up in Senate question time, Morrison was clear in the House of Representatives that the net zero decision would be taken by cabinet.

Morrison said that process aligned with “the approach taken in the past” when it came to setting Australia’s international climate commitments – like agreeing to the Kyoto and Paris agreements.

Any ministers dissenting from the cabinet decision would need to consider their positions.

The Nationals are split about whether to agree to net zero and a handful of trenchant opponents, including Queenslanders Matt Canavan and George Christensen, are campaigning actively against that landing point.

While a group of Nationals remain implacably opposed, senior Liberals and Nationals remain hopeful the impasse will be resolved.

The Nationals leader, Barnaby Joyce, has appointed a kitchen cabinet of four Nationals ministers, which includes McKenzie, to work up a wishlist in exchange for supporting the mid-century target. Joyce told parliament on Wednesday that list would be with Morrison in the next 24 hours.

While Nationals opposed to net zero will push for poison pill items, like new coal plants, party MPs have been told the wishlist should not include specific projects – like power plants, or local roads and bridges – but instead reflect principles and safeguards protecting regional Australians during the transition.

David Littleproud, the agriculture minister, supports an “aspirational” net zero target. He told the ABC on Wednesday: “We are not working through parochial projects.”

“We are thinking more about how we secure regional and rural Australia’s future if [net zero] is imposed and how do we grow it as part of it,” he said.

Littleproud said the principles outlined in the wishlist would be more about using existing mechanisms and programs for regional employment and jobs “than going for a cash grab”.

But when questioned whether the eventual ask from the Nationals would include money, Littleproud responded: “Money makes the world go around.”

In the lower house, Joyce said the Nationals were working through a collaborative process – not “grandstanding”.

Asked about McKenzie’s warning shot at Morrison, Joyce said the Nationals were following a prudent and constructive internal process. Joyce said the Nationals party room would be the “final arbiter … of our position”.

During question time, Joyce expressed scepticism that renewables projects generated substantial numbers of jobs.

When it was pointed out to Joyce that Australia’s mining, farming and livestock industries supported a net zero target, Joyce acknowledged that BHP and Rio Tinto were supportive, as was the National Farmers Federation, but he said senior business leaders inhaled “rarefied air”.

Joyce said executives did not live in mining towns like Muswellbrook or Singleton in the Hunter Valley. He also noted that farmers only made up 12% of his electorate of New England.

While again telegraphing that the cabinet, and not the Nationals party room, was the decision-maker on net zero, Morrison sought to soothe rather than inflame Coalition tensions on Wednesday afternoon.

The prime minister said he understood that people in rural and regional Australia “will face some real challenges to their economic futures because of what is happening around the world, and changes in the global economy”.

He said it was important not to engage with opponents of the transition in “any sort of pejorative way”.

It is possible the Nationals party room will meet again this week to consider the final wishlist. Once that list is finalised, Joyce will meet again with Morrison. The Nationals are also due to meet this coming Sunday. Federal parliament sits again next week.

Assuming the Nationals wishlist is acceptable to Morrison and the Liberals, cabinet and the joint Coalition party room will meet next week.

Rio Tinto said on Wednesday it will switch its iron ore mines in the Pilbara to renewables as part of the multibillion-dollar pledge to accelerate decarbonisation.

The move, announced to investors on Wednesday evening, would see gas phased out at the company’s Pilbara mines and coal eliminated from the electricity supply to its aluminium smelters. It has warned that the future of its Australian smelters, at Boyne Island and Tomago, depends on being able to decarbonise their power supplies.