The NSW Nationals will write to 20 members asking them to justify why they should not be expelled from the party over their alleged links to white supremacist and alt-right movements.

Key points: NSW Nationals admit it is "impossible" to track down all members with extremist views

NSW Nationals admit it is "impossible" to track down all members with extremist views The party's state director said he has noticed a change in the type of people joining the party

The party's state director said he has noticed a change in the type of people joining the party They do not expect to kick 20 people out of the party

But the party's state director Ross Cadell admitted it was impossible to track down and get rid of all members with extremist views.

The party has investigated about 35 members, after the ABC revealed a push by people involved in the alt-right movement to join mainstream Australian political parties, in order to influence their policy agendas from within.

Some of those under investigation allegedly shared social media posts praising the Holocaust and Hitler, while others have been pictured in photos posing in white-power symbols.

Mr Cadell said it was likely 20 people would receive letters asking them to explain their actions.

"We would hope to write to them and have them justify why they should remain members of the National Party," Mr Cadell said.

He said he expected "almost certainly some will be facing expulsion," but not all of those who will be sent letters were implicated to the same level.

"Some of them have partaken in hate speech and some of them haven't," he said.

"But they are linked closely enough that we want to get some understanding of where they are and that's what we hope to do.

"There's a photo of them pulling alleged white power symbol at a dinner table and there's some members of the party that were just sitting there.

"They aren't pulling the same symbol, but they are doing hand gestures and we just want to clarify where they are, what they're doing and what is their involvement, if any."

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Mr Cadell said he had, before the investigation, noticed a change in the profile of people joining up to the Young Nationals.

He said the Nationals were sharing information with "at least one other political party" that it may too have been infiltrated.

He did not name the party, but said it was not the Liberal Party.

The Nationals state director said it was impossible to be sure that no other members of the Nationals sympathised with neo-Nazi views.

"I think in any political party where you've got almost 10,000 members, you're going to have people who are sleepers from all sorts of beliefs," he said.

"The difference to us is that this is about those who engage in hate speech and as soon as they pop up we have to get them quickly but if they hold different beliefs and they hold them quietly, they're almost impossible to find."