Former Nationals leader Barnaby Joyce has come out swinging against his party's alliance with the Liberals.
Mr Joyce has described the coalition as a marriage of convenience that diminishes the electoral prospects of both parties.
He says the Nationals are berated if they talk to constituents about issues at odds with coalition policies, describing many as merely Liberal Party platforms.
Deputy Prime Minister Michael McCormack has been forced to defend the coalition.
"Seeing as though he used the word of marriage, it's a marriage of strength. We work well together," Mr McCormack told reporters in Canberra on Wednesday.
The public spat could create problems for Mr McCormack when federal parliament returns next week, with a grumbling rump of Nationals MPs unhappy with his leadership.
It could also exacerbate existing tensions inside the coalition joint partyroom.
Mr Joyce's criticism comes after Nationals backbenchers released a manufacturing plan underpinned by more investment in coal-fired power stations.
The blueprint has stirred tensions within the coalition and created a headache for Prime Minister Scott Morrison, who is under increasing pressure at home and abroad to take stronger action on climate change.
Mr McCormack is open to throwing government money at new coal plants.
"If states and indeed private players say to us that yes, this is an option going forward, well yes we'll absolutely look at it," he said.
But Treasurer Josh Frydenberg has flatly ruled it out.
"We're not about to do that - we're not about to fund a new coal-fired power station," he told ABC radio.
"What we are in the process of doing is encouraging security of supply, more affordable power and reducing our carbon footprint."
Mr Joyce also argued Nationals MPs should hold crucial portfolios such as trade, treasury or defence.
"I am kicking up the dust now because the coalition has devolved into a marriage of convenience that diminishes the electoral prospects of the whole coalition," he wrote in The Australian.
"This needs to be corrected prior to an election, which I presume will be at the end of this year. A coalition has to be in fact and form to authentically live up to its name."
Mr Frydenberg said the coalition had been "very successful" and the Nationals had increased their support at the last election.
"What we have seen is Scott Morrison and Michael McCormack being a very strong partnership that has delivered jobs and support through the COVID pandemic for regional Australia, indeed for broader Australia," he told reporters in Canberra.
Australian Associated Press
