Nationals volunteers, including a staff member in deputy premier John Barilaro's office, have been wearing fluorescent orange vests and handing voters a leaflet informing them: "You don't need to number every box".

Labor alleges the tactic is aimed at tricking voters into believing they are distributing official NSW Electoral Commission material.

The Nationals' are running a "Just Vote 1" strategy in the byelections in a bid to reduce the number of preferences that might flow to the Shooters candidates who are their main threats in the seats.

The Berejiklian government has released draft legislation that would introduce a new offence of prohibiting a person from displaying material that "falsely appears to have been authorised by the Electoral Commission or Electoral Commissioner".

NSW Labor general secretary Kaila Murnain said: "The National party has been up to their same old dirty tricks during these byelections, showing their desperation to retain the seats of Murray and Cootamundra".

"The Nats have taken these areas for granted for way too long," she said.

Robert Borsak, head of the Shooters, Fishers and Farmers party, said the Nationals staff had been "caught red-handed" giving out illegal electoral material, with the official reprimanded by the NSW Electoral Commission.

"They knew it was in breach of the Electoral Commission's rules but they did it anyway," Mr Borsak said. 

"This is another example of the arrogance we've seen from the National Party in the Cootamundra by-election," he said. "They've tried to dupe voters with dodgy scare campaigns and now it's back-fired."

But Nationals state director dismissed the allegations as "election day scuttlebutt".

"Labor tried to imitate NSW Electoral Commission branding at the last state election," he said. "I'm quite surprised they haven't tried to do it again."

Labor has also accused the Nationals of handing out unregistered electoral material in the form of an open letter signed by former prime minister John Howard and deputy prime minister Tim Fischer warning about the gun control policies of the Shooters, Fishers and Farmers party.

The Shooters' policy is to repeal the national firearms agreement introduced by the Howard government which would mean greater access to high powered semi-automatic weapons and pump action shotguns.

Mr Barilaro's staff member - who Fairfax Media has chosen to not name - was spoken to by officials in Young after Labor reported the matter to them but it is unclear if any action was taken. The NSW Electoral Commission has been contacted for comment.

Premier Gladys Berejiklian flew into Griffith in the seat of Murray on Saturday morning, while Mr Barilaro has visited Griffith and Cootamundra.

The byelections are being held following the retirement from politics of former Nationals ministers Adrian Piccoli and Katrina Hodgkinson.

A third byelection - which Labor is expected to win comfortably - is being held in the Sydney seat of Blacktown after former NSW ALP leader John Robertson retired from parliament.