Scott Morrison is facing pressure to attend a major global climate change conference where Australia is expected to increase its emissions reduction goals.
The coalition government has been tiptoeing towards adopting a 2050 net zero greenhouse gas target ahead of November's COP26 talks in Glasgow.
Labor leader Anthony Albanese said the prime minister should commit to travelling to the United Nations climate change conference.
"He should represent Australia. If he doesn't, it's because he's embarrassed about Australia's position," Mr Albanese told reporters on the NSW Central Coast on Monday.
Foreign Minister Marise Payne said attending the conference was a significant undertaking but insisted Australia would have a senior representative at the talks.
"It involves the two-week domestic quarantine as well. So no final decisions have been made," she told ABC radio.
While the government is planning on releasing a long-term emissions reduction plan before COP26, the Nationals have so far stood in the way of the 2050 commitment.
Mr Morrison said he had not made a final decision about attending COP26, which is considered the most important global climate conference in years.
"I mean it is another trip overseas and I've been on several this year and spent a lot of time in quarantine," he told the West Australian newspaper
"I have to focus on things here and with COVID. Australia will be opening up around that time, there will be a lot of issues to manage and I have to manage those competing demands."
The prime minister on Sunday started two weeks of quarantine after returning from the US.
He has also travelled to the UK, France, Singapore, New Zealand and Japan during the pandemic.
Deputy Prime Minister Barnaby Joyce, who met with Nationals colleagues online on Monday, said the net zero target remained "an item of discussion".
Asked on the ABC when a final decision might be reached, he said: "When the party room decides they've come to that conclusion. And we'll follow that process along."
He said his party understood in the long term "there may be a transition to other fuel sources", but he and his colleagues would never put the coal industry at risk.
"We have to make sure we are part of that transition, but any jump off a cliff now will just put Australia in a financially perilous position," he said.
Finance Minister Simon Birmingham said there were environmental and economic grounds to support the target.
"There's many reasons why Australia does need to chart the course to net zero," the senior Liberal cabinet minister told Triple M.
Nationals senator Matt Canavan has declared he is "dead-set against" the target, a position fellow Queenslander George Christensen holds.
Deputy Nationals leader David Littleproud said the party would need to see any detail before it committed to a plan.
"The fact is, regional Australians have paid most of the bill for reducing emissions," he told the Nine Network.
"We've paid that bill. It is time to square the ledger."
Resources Minister Keith Pitt is remaining tight-lipped about the prospect of the junior coalition partner supporting a 2050 goal until a proposal comes before the party room.
Victorian Nationals MP Darren Chester, who it taking a break from the party, said Australia needed a plan to reduce emissions.
Australian Associated Press