NSW Deputy Premier John Barilaro has reportedly accused Riverina MP Michael McCormack of having "failed as a leader" during a series of purported text messages over the Eden-Monaro byelection.
Mr Barilaro this week ruled out an attempt to switch from state to federal politics via a three-cornered race with the Liberals and Labor for retiring MP Mike Kelly's electorate.
However, Sky News reported on Tuesday afternoon that leaked messages from Mr Barilaro to Mr McCormack, who is Deputy Prime Minister and federal leader of the Nationals, claimed a lack of support for seeking preselection.
"Don't hide behind the "members will choose the candidate' rubbish, as you were the only one saying such lines," Sky News reported Mr Barilaro's messages as stating.
"Don't you think my branches would have backed me in?
"To feel threatened by me clearly shows you have failed your team and failed as a leader.
"You will never be acknowledged by me as our leader. You aren't. You never will be."
Mr Kelly resigned from parliament last week citing ill health, having held the bellwether seat for Labor for two of three terms since 2007.
Most byelections in Australia have been lost by incumbent governments but Mr Barilaro previously claimed National Party research showed he could have won.
"The Nats had a chance to create history, to change momentum, and you had a candidate that was prepared to risk everything to make it happen, Sky News reported Mr Barilaro's messages to Mr McCormack as stating.
"What did you risk? Nothing. Hope you are proud of yourself."
The Daily Advertiser has sought comment from Mr McCormack.
Mr McCormack told Sky News he had "never done anything but provide support" to Mr Barilaro.
"I have never done anything but provide support for John Barilaro ... he's been great for regional NSW," he told the TV network.
"I gave him fulsome support. I still did say the local branches would have to endorse him. I have never given away the autonomy of local branches."