A star Labor candidate contesting one of the state's most marginal seats is under investigation for allegedly assaulting his female flatmate.
NSW Labor has directed its candidate review committee to investigate an anonymous complaint it received about the mayor of Muswellbrook, Martin Rush, who is running in the seat of Upper Hunter.
Upper Hunter is one of the Nationals' most marginal seats and one that Labor is expected to win in the March state election.
But the emergence of the anonymous letter outlining details of the alleged incident throws Labor's chances in the must-win seat into doubt.
The letter was sent to the Leader of the Opposition Michael Daley on December 21, as well as NSW Labor's head office.
The letter outlines an alleged incident between Mr Rush and his female flatmate, who he shared a house with along with her partner. The complaint alleges Mr Rush came home heavily intoxicated on September 8 last year. It alleges Mr Rush and his flatmate were involved in a heated argument that ended in him "gripping as tightly as he could, shook her, whilst screaming awful things at her".
The letter alleges the flatmate had bruising on her arms.
Mr Rush has been contacted for comment. He did not respond to the Herald. The matter remains subject to investigation, and the Herald does not suggest that allegations raised against Mr Rush in the anonymous letter are in fact true.
A spokeswoman for NSW Labor confirmed an anonymous complaint had been received.
"In accordance with the Labor Party’s internal processes, Party Officers referred the complaint to the Candidate Review Committee for consideration," the spokeswoman said.
"That process is well advanced and will be finalised as soon as is reasonably possible. The Labor Party takes these matters very seriously."
The candidate review committee is chaired by party elder and former deputy premier, John Watkins.
The incident was also reported to police.
A spokesman for NSW Police said: "On Friday 7 December 2018, police were made aware of an alleged incident between a man and a woman who are known to each other, believed to have occurred in September 2018.
"Officers from Hunter Valley Police District conducted inquiries into the allegations, however no statement was provided to police. As a result, no further action is pending."
Mr Daley's office also confirmed they received the anonymous letter.
"On Friday 21 December 2018 (the last working day before the Christmas break) an anonymous letter was received in Mr Daley's electorate office. Staff in the electorate office passed it on to our Chief of Staff, Kris Neill," a spokeswoman said.
"As dealing with complaints about candidates is a matter for the administrative wing of the Labor Party, on the same day Ms Neill referred the letter to the Governance Director of NSW Labor, for immediate investigation."
The Nationals hold Upper Hunter with a margin of 2.2 per cent. The party fears it could lose the seat, along with Lismore, Tweed and Barwon, to Labor or the Shooters, Fishers and Farmers Party.
The Coalition only holds a six-seat majority and the loss of four Nationals seats, as well as the possible loss of the Liberal seats of East Hills and Coogee, could put them in minority government.