The development is a new headache for the minority Napthine government, which already relies on the vote of Independent MP Geoff Shaw to get laws through Parliament.

Mr Crisp has been charged with keeping unregistered guns at his farm, on the NSW side of the Murray River, News Corp reported.

Keeping an unauthorised prohibited firearm is an indictable offence drawing up to a maximum 14 years' jail.

If Mr Crisp is convicted or found guilty of an indictable offence carrying a penalty of five years imprisonment or more, he would be ineligible to sit in state Parliament, meaning there will have to be a by-election for his seat of Mildura.

Mr Crisp said he has always held the appropriate firearms licences in NSW and Victoria and and his firearms have been properly registered at all times.