A Coalition senator says the Liberals must not become “One Nation lite” to combat the threat of Pauline Hanson’s party, which has been bolstered by Barnaby Joyce’s defection from the Nationals.

The New South Wales senator and leading moderate Maria Kovacic has conceded Joyce’s decision to join One Nation to lead its Senate ticket in the state made it “much more challenging” for the Liberals to retain all of their seats.

The Coalition run a joint Senate ticket in NSW, which at the 2028 ballot is expected to place the Liberals in the first and third positions, with the Nationals at number two.

After snatching the sixth NSW Senate seat at the May election with 6% of the primary vote, support for One Nation has roughly doubled nationally according to various opinion polls.

While cautioning that the support might not hold up until 2028, independent psephologist Kevin Bonham said One Nation would be a serious chance of securing the third Coalition seat even if its vote was only marginally higher than at the May ballot. That would put the second Liberal at senior risk.

Kovacic and fellow moderate Dave Sharma are the two Liberal senators up for re-election in NSW in 2028.

As the Coalition grapples with the rising popularity of One Nation and brace for an electoral fight against Joyce, Kovacic said Liberals must not attempt to mimic the populist party.

“That third position that Barnaby Joyce and One Nation will now be contesting for, or trying to gain, it will be much more challenging for us to retain that spot,” Kovacic said.

“But regardless, that is something we will fight to do. But in doing so, we need to focus on that fact that in the same way that people talk about us not being Labor lite, we also need to understand that we cannot be One Nation lite. We need to be Liberals because that is who we are.”

Kovacic said that meant developing policies focused on “sensible and practical outcomes”, not one that was “centred in populism”.

After following Hanson in dumping a net zero emissions target, the Coalition is now debating One Nation’s other main preoccupation: cutting immigration.

The opposition is expected to this week unveil a set of “principles” to guide its migration policy and how it would determine intake numbers, although it won’t yet set targets for net overseas migration.

Guardian Australia last week reported anxiety among Liberal MP about the language being deployed in the debate, particularly the phrase “mass migration”.

Joyce claimed Hanson had “driven the political agenda”, crediting her with causing the Liberals and Nationals to abandon their net zero emissions target.

“I’m philosophically aligned with One Nation. I’m a conservative and I’m not embarrassed about it,” he said in a joint radio interview with Hanson on Monday in which he confirmed his defection.

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The former deputy prime minister’s switch to One Nation had been on the cards for weeks after a bitter public fallout with the Nationals, in particular leader David Littleproud, who dumped Joyce from the frontbench after effectively sidelining him during the 2025 election campaign.

Littleproud described Joyce’s decision to abandon the Nationals to join a “party of protest” as “disappointing”.

“The Nationals supported Barnaby through many difficult times, including during his darkest moments,” he said.

“Barnaby has chosen to turn his back on the Nationals and on his electorate and instead join a party of protest, which is never able to achieve anything other than headlines.

“I have never had a personal issue or problem with Barnaby Joyce. This issue is about Barnaby wanting to be the leader of a party.”

Joyce has built a loyal support base in New England since switching from a Queensland Senate seat in 2013, repeatedly defying scandal and controversy to retain his place in Canberra.

He gained a 1.85% swing at the May election, extending his margin to 17%.