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Voters turning to minor parties have the big two scared

No election would be complete without a scare campaign about voting for independents and minor parties.

And with only two weeks left until polling day in NSW, Labor and the Liberals are pulling out all the stops, desperate to convince people to stick with them.

Political pasts and preference swaps have become fair game, with Treasurer Matt Kean taking the partisan barbs to a creative new level.

He accused One Nation leader Mark Latham of being a sleeper agent for the party he took to the federal election in 2004.

"What we're seeing is Mark Latham's true agenda here," Mr Kean told reporters.

"He wants a Labor government."

The treasurer spread similar messages on social media, contending a vote for Mr Latham was a vote for Labor. Electoral analyst Kevin Bonham said there was no truth to the claim.

"A vote for a candidate is a vote for that candidate," Dr Bonham told AAP.

"The voter can then decide to preference other parties if they choose to do so."

Unlike in federal elections, NSW voters are only required to number one candidate on their lower house ballot.

If that candidate is excluded, their vote exhausts and is not transferred to other election contenders.

Dr Bonham said One Nation voters were more likely than most to number only one box, meaning in tight contests the coalition could lose conservative votes that would ordinarily flow to them over Labor.

"We know from the federal election that if One Nation voters had distributed their preferences they would tend to favour the coalition," Dr Bonham said.

One seat where a split in the conservative vote could be costly is Kiama, where the Liberals are running a candidate against sitting MP Gareth Ward.

Labor is also trying its hand at creating a bit of preference panic in the seat of Balmain, claiming that preferencing the Greens risks a return to coalition rule.

Dr Bonham said the claim was vague but it seemed to suggest the more seats the Greens held instead of Labor would diminish its chances of forming government.

Even still, the Greens would more likely back Labor than the Liberals in the event of a hung parliament, so the argument was largely irrelevant.

"They're greatly overstating it when they say that Labor must win the seat of Balmain," he said.

Labor and the coalition have haemorrhaged votes to minor parties in recent elections, increasing the odds they will have to negotiate with an enlarged cross bench to form government.

At the last election in 2019, three quarters of voters put either Labor, Liberal or National as their first preference - down from 95 per cent in 1981.