NSW Premier Mike Baird, former premier Nick Greiner and Howard government minister Amanda Vanstone have delivered a blow to Bronwyn Bishop's hopes of staying in Parliament for another three years.
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Amid growing talk in Liberal Party ranks that Ms Bishop has lost control of the outcome of her preselection, the influential trio have given their blessing to the former speaker's main rival, Jason Falinski.
In reference letters obtained by Fairfax Media, Mr Baird, Ms Vanstone and Mr Greiner laud Mr Falinski's "entrepreneurial skill".
In his letter, sent to preselectors on Friday, Mr Baird said Mr Falinski, a former president of the Young Liberals, understood through his private sector experience what "leads businesses to invest and grow" to the benefit of the economy.
"I have found in public life that these insights are all too rare, yet have never been in greater need," Mr Baird wrote.
His focus on Mr Falinski's business experience is likely to be interpreted as a swipe at Mrs Bishop, who has spent almost three decades in Parliament and in Liberal Party positions before that.
As revealed by Fairfax Media in December, the former speaker, 73, told local supporters that she was needed in Parliament - in part to help fight the threat of terrorism.
Her influence over Liberal branches in the northern Sydney seat of Mackellar has long been described as "North Korean" in its dominance but there is growing signs her support is on the wane.
In the estimate of one factional player, she currently has fewer than 30 of the 96 preselectors needed to remain the Liberal candidate.
Walter Villatora, a member of the hard right who has the backing of former prime minister Tony Abbott, is believed to have about 15 votes.
Mr Falinski, who is a member of the dominant moderate faction in the NSW Liberals, could command more than 30 votes and Fairfax Media understands the hard right would swing in behind him if Mr Villatora ends up out of the race.
We need our supporters most in tough times so those who stick with us earn a big tick from me
The hard right is gunning for Mrs Bishop, who has enjoyed the backing of the centre right, in retaliation for her "turncoat" decision to abandon Mr Abbott and vote for Malcolm Turnbull in the September leadership change.
The preselection vote will take place on Saturday, April 16. The 96 preselectors will be made up of 48 votes local branch delegates, 29 representatives of the Liberal state council and 19 members of the state executive.
Mr Falinski, a longtime factional player who spent four years on Warringah Council and was involved in the successful 2007 election campaign that resulted in Liberal Rob Stokes taking the state seat of Pittwater back from independent Alex McTaggart.
Mr Falinski founded CareWell Health 12 years ago.
Ms Vanstone described Mr Falinski as a "true believer" in the Liberal cause, saying he is "not just a fair weather friend".
"We need our supporters most in tough times so those who stick with us earn a big tick from me," she wrote.
Fairfax Media revealed in February that influential broadcaster and former supporter of Mrs Bishop, Alan Jones, has thrown his support behind former Wallaby Bill Calcraft.
Mr Jones coached Mr Calcraft, a former businessman, during the 1984 Grand Slam Wallabies tour of Britain and Ireland.
"Let me say bluntly, there could be no better candidate," Jones wrote.
"He is a born leader. He has a manly sense of the fitness of things. He is highly regarded by his peer group. He has an incisive mind and an intellect which embraces the detail of matters political and non-political at an international and domestic level.