Deputy Premier John Barilaro announced in Port Macquarie on Tuesday that his party would preselect a candidate next year, ahead of the NSW election in March 2023.

The unusual declaration will reignite tensions within the already frail coalition. It comes just a few months after Mr Barilaro backed down from a threat to move to the crossbench and stop supporting government legislation over a koala policy.

Port Macquarie is held by Leslie Williams, who defected to the Liberal Party from the Nationals in November.

Mr Barilaro said on Tuesday that the National Party had been "betrayed" and that the Liberals had "actively" wooed Ms Williams.

Ms Williams opposed Mr Barilaro's handling of the koala dispute and called his threat to move to the crossbench "unnecessary, unhelpful and frankly politically reckless and unreasonable" when she announced her defection.

Ms Williams has held the seat since 2011.

The coalition agreement prevents the two parties from running against each other, but Mr Barilaro said voters had elected a National candidate.

"The only party that has done any damage to the Coalition is the Liberal Party," Mr Barilaro said.

"This is about the people of Port Macquarie and giving them the best possible representation," he tweeted on Tuesday.

"The NSW Nationals stand for a stronger and safer Port Macquarie, and a stronger and safer regional NSW.

"The people of Port Macquarie deserve to make this choice."

Australian Associated Press