Prime Minister Scott Morrison has announced the Liberals will preference One Nation below the Labor Party at the federal election.

Key points: Mr Morrison said he discussed preferences for One Nation with former PM John Howard

Mr Morrison said he discussed preferences for One Nation with former PM John Howard One Nation has been engulfed in a scandal surrounding foreign donations and weakening gun laws

One Nation has been engulfed in a scandal surrounding foreign donations and weakening gun laws Secret recordings appear to show Pauline Hanson questioning the Port Arthur massacre

The commitment comes after an Al Jazeera investigation revealed One Nation tried to solicit millions of dollars in donations from a US gun lobby last year.

That same investigation has obtained footage of the party's leader Pauline Hanson appearing to suggest the Port Arthur massacre was part of a conspiracy.

Mr Morrison has faced repeated calls for the Coalition to preference One Nation last at the election.

His comments today relate to candidates running under the Liberal banner and it will be for the Nationals, the junior Coalition partner, to decide its own preferences for its candidates.

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The National Party is so far refusing to follow the Liberal preferencing decision, with leader and Deputy Prime Minister Michael McCormack saying a decision will be made closer to the election.

"When it comes to preferences, as is the case with every election, the Nationals are a grassroots party and decisions are made at a state and local level," he said in a statement.

"These decisions will be made closer to election day when all the candidates are known."

The Coalition exists as a single party in Queensland, called the Liberal National Party (LNP).

LNP politicians who sit in the Liberal partyroom will follow Mr Morrison's directive and preference One Nation below Labor.

However, the ABC has been told LNP politicians who sit in the Nationals partyroom will be able to decide for themselves, with Ken O'Dowd, Keith Pitt and Michelle Landry all having previously said they would preference One Nation above Labor.

Mr Morrison said he had discussed preferences for One Nation with former prime minister John Howard, who overhauled Australia's gun laws following the 1996 Port Arthur massacre.

At the time, Mr Howard demanded One Nation be preferenced last on how-to-vote cards.

"In the same way that he [Mr Howard] indeed did not rush into this decision when he took it 20 years ago, I followed a similar process," Mr Morrison said.

"I was waiting to see what their reaction would be earlier in the week and I was disappointed by that reaction."

Labor demands Coalition put One Nation last on how-to-vote cards

Labor leader Bill Shorten said he was "deeply concerned" the LNP and Nationals "appear to have a pass" from the Prime Minister's directive, which would allow for "secretive preference deals with One Nation".

He again demanded the Coalition put One Nation last on how-to-vote cards.

"This is sneaky. He [Mr Morrison] can't bring himself to put One Nation last because he wants their preferences if he can get away with it," Mr Shorten said on Twitter.

"These are Government members and Coalition candidates and the Prime Minister needs to pull them into line.

"You can't pretend to stand up for middle Australia while your Government colleagues are swapping preferences with conspiracy theorists and con men."

Mr Morrison has repeatedly said the Coalition would not enter into preference deals with One Nation.

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Senator Hanson, besides posting a statement on Twitter, has not publicly commented on the scandal that has engulfed her party.

It remains unclear whether One Nation will preference the Coalition and Labor on its how-to-vote cards, with the party's preferences having been crucial to helping both sides get MPs elected in the past.

NSW One Nation MP Mark Latham, the former federal Labor leader who was elected to the State Parliament Upper House at the weekend, warned retaliation action from his party would cost the Liberals seats at the May federal election.

He listed the NSW federal seats of Banks, Gilmore, Hughes, Robertson, Riverina and Parks as having benefitted from One Nation preferences in the past.

The ABC will broadcast the second part of the Al Jazeera documentary tonight.

In the episode, footage shows Senator Hanson discussing Port Arthur with her chief of staff James Ashby and undercover journalist Rodger Muller at a dinner in the central Queensland town of Yeppoon.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 8 seconds 1 m 8 s One Nation's Pauline Hanson and James Ashby on a hidden camera

"An MP said it would actually take a massacre in Tasmania to change the gun laws in Australia," she told Mr Muller, who was posing as a gun rights advocate.

"Have you heard that? Have a look at it. It was said on the floor of Parliament.

"Those shots, they were precision shots … they didn't muck around … I read a book on it, on Port Arthur. A lot of questions there."

Debate has raged in Australia about gun policies following the One Nation revelations and Christchurch mosque massacre.

Cabinet minister and deputy Nationals leader Bridget McKenzie, a avid supporter of recreational sport shooting, said it was crucial people following the law not be dragged into the current debate.

She urged people against "conflating law abiding citizens participating lawfully in their sport with an extreme terrorist".

"Too often I think law abiding shooters and the businesses, over 1,000 small businesses, that actually employ Australians and support our sporting shooters and our farmers indeed to use their firearms responsibly are demonised in this country and they shouldn't be," Senator McKenzie said.

Watch the second part of the Al Jazeera investigation on tonight on ABC TV or watch the full documentary on iview.