Nationals Leader Michael McCormack has defended his party's decision to preference One Nation above Labor and the Greens, saying they are "more aligned" with Pauline Hanson's party.

Speaking at the National Press Club, the deputy prime minister was blunt about the reason for the deal as the Nationals battle to hold several key marginal seats at the 18 May election.

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"You have to do what it takes to get votes and to win at an election," he said.

"The fact is that the National Party policies, probably closer align with One Nation, than they ever will with the Greens or Labor."

His comments appear to contradict Prime Minister Scott Morrison, who directed the Liberal Party to preference the minor party below Labor after it was revealed senior figures had flown to the US and discussed watering down Australia's gun laws with the National Rifle Association.

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At the time, Mr Morrison said he was disappointed by the party's response to the scandal and was shocked by Ms Hanson's reference to a conspiracy theory about the Port Arthur massacre.

Mr McCormack was speaking just hours after Steve Dickson resigned as a One Nation Senate candidate in Queensland over his behaviour at a strip club during the same trip.

"I appreciate that some members of One Nation have done some rather interesting things lately, and said some things that are quite unpalatable," he said.

He said that while journalists were "obsessed" by preferences, that he was rarely asked about it on the campaign trail.

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As early voting got underway this week, the PM has been defending the Liberal Party's preference deal with Clive Palmer's United Australia Party.

The deal which sees Liberals put the far-right minor party second or above Labor in all seats almost guarantees the mining magnate's return to Parliament.

At the same time the federal government is pursuing Mr Palmer in the court over unpaid payments to former employees of his nickle mine.

Mr Morrison said Labor and the Greens are a bigger risk to Australia.

"Because Labor and the Greens are going to put a 45 per cent emissions reduction target on Australia which is going to cost some $475 billion over the next 10 years," Mr Morrison told reporters on Tuesday.