A man has been charged with making a threatening phone call to the NSW Nationals office on the day the party moved to expel white supremacist elements from its ranks.

Key points: A 55-year-old man was charged by NSW Police

A 55-year-old man was charged by NSW Police The NSW Nationals will meet next week over concerns of party infiltration by neo-Nazis

The NSW Nationals will meet next week over concerns of party infiltration by neo-Nazis At least 35 members are under investigation over white supremacy links

The National Party called police after a man phoned its Sydney head office on Pitt Street and allegedly threatened staff on Monday morning.

At the time, the party officials were meeting to discuss sending letters to 20 members asking them to justify why they should not be expelled from the party for alleged links to neo-Nazi materials.

Police arrested a 55-year-old man at a home in Chippendale yesterday and charged him with using a carriage service to threaten, harass and intimidate.

He was granted strict conditional bail and will appear at Downing Centre local court next month.

Senior Nationals Minister Melinda Pavey said the alleged threat would not deter her party from investigating those with suspected links to white supremacy.

"We've just got to do what we've got to do, you can't not do something because you're afraid — that's not us, that's not the Nationals," she said.

"We don't have truck with any of that type of behaviour," she said.

"I've not seen that type of behaviour before and I'm pleased that our party has called it out and has the investigation ongoing."

The ABC understands the party will meet again later this week.

The party has investigated at least 35 members since the ABC's Background Briefing revealed a plot by members of the alt-right movement to infiltrate and influence Australian political parties from within.

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

"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."

He said it was important to send a strong message that anyone known to have links to white supremacist movements would not be tolerated within the party.