"Time to go, Barnaby, and don't come running to Hancock for a job after the people wise up to you."

Mr Hancock told The Australian Financial Review he was a Coalition voter and supported Prime Minister Malcolm Turnbull and deputy Liberal leader Julie Bishop.

"Barnaby needs to go... Australia simply deserves better, and we can do better, surely," he said.

Mr Joyce intervened in the Rinehart family's bitter legal dispute in 2011, advising Mr Hancock's siblings to keep the dispute out of the media.

John Hancock says Barnaby Joyce had used a position of advantage and caused pain to his own family and former staffer Vikki Campion. Philip Gostelow

The long-running legal battle started in September 2011, days before Mrs Rinehart's youngest daughter, Ginia, was due to turn 25 and a $4 billion trust was due to vest.

"All good families have their problems but before it gets really out of hand, I would try to get it back in house and out of the public view," Mr Joyce wrote.

"Your family are good people. If they were not I would not care as much about you and your Mum."


High-profile supporter

Mrs Rinehart has been a high-profile supporter of Mr Joyce, last year awarding him a $40,000 prize for his support of Australian farming and agriculture.

David Rowe

Mr Joyce handed back the award in November, received when he was agriculture minister and fighting a by-election in his seat of New England sparked by his dual citizenship.

After telling the ceremony he would use the money for projects on his farm, Mr Joyce said a day later he had taken immediate action "to politely decline any acceptance" of the prize.

The mining magnate donated $50,000 to Mr Joyce's 2013 election campaign and employs former Liberal frontbencher Sophie Mirabella and former Northern Territory chief minister Adam Giles in her company.

Hancock Prospecting did not respond when contacted for comment.

Barnaby Joyce intervened in the Rinehart family's bitter legal dispute in 2011, advising John Hancock's siblings to keep the dispute out of the media. AAP

Facing the threat of a leadership challenge, Mr Joyce apologised to everyone involved in his affair this week and told colleagues on Tuesday night he intended to fight on.

Senior party sources have said Mr Joyce's future hinged on whether he could quickly recover. He is due to be acting Prime Minister next week as Malcolm Turnbull travels to the United States.