He wants the unemployment benefit payment boosted, and joins economists, social-welfare groups and others pushing the change in the face of blanket opposition from the Coalition government.

His party's policy committee has also defied the Prime Minister by secretly conducting their own costings on boosting the allowance. They will model the economic impact of raising the unemployment benefit, but quarantining 80 per cent of the payment on a cashless welfare card, which can only be used for essentials.

Mr Joyce's push comes despite Prime Minister Scott Morrison urging unity on the party room last week, telling MPs not to "run off" in public with issues the government didn't take to the election but to raise policy ideas internally.

Two Liberal backbenchers, Russell Broadbent and Dean Smith, have also broken ranks to support an increase in Newstart.

On Thursday, the Senate launched an inquiry into the payment, which will ensure the issue remains front and centre for months. The inquiry accepts submissions till September 13 and reports at the end of March next year.

Newstart for singles is $278 a week, and has been tied to inflation instead of wages since 1997. The Greens want to boost it to $353 a week, which is where it reportedly would be if it had been pegged to wages like the pension.

The Business Council of Australia has backed an increase, with chief executive Jennifer Westacott saying people have no capacity to pick themselves up and get back in the workforce if they lived in real poverty, unable to buy interview clothes, homeless and in poor health.

Greens Senator Rachel Siewert, moving for the inquiry in the Senate, said after paying for accommodation, Newstart recipients were left with just $17 a day. She pointed to analysis from Australian National University Professor Peter Whiteford showing Australia's unemployment payment was second lowest in the OECD.

The inquiry was supported by crossbench senators Stirling Griff and Rex Patrick (Centre Alliance), Pauline Hanson and Malcolm Roberts (One Nation), and Jacqui Lambie. It will investigate widely, including looking at insecure work, the impact on older people, people with disabilities, migrants and people living in remote areas, and the overall adequacy of income support payments. It will consider whether a separate body could be used to set payments, taking it out of the hands of politicians. And it will look at the cost of boosting Newstart, the Greens' push for an extra $75 a week estimated to cost the budget $3 billion a year.

Mr Joyce, writing in The Canberra Times, said Newstart was one of three new issues he wants to push this term. People were being put out of work in small towns because of the drought and they could not survive on Newstart, he said.

St Vincent De Paul, among many other groups, had urged his help.

"They want to hear your advocacy, they want to see it If required, they want to see you punched in the nose because of it," he said.

Mr Joyce said he was metaphorically punched in the nose when he called for Australian Guantanamo Bay detainee David Hicks to be brought back to Australia to face trial. He was the only Coalition MP to sign a letter spearheaded by the Labor and the Democrats urging Mr Hicks's release.

His advocacy was not about Mr Hicks, of whom he had a dim view, but his belief that he was entitled to a fair trial, and that Australia should not be "a lickspittle to an alternative agenda of another nation".

"You get in strife speaking up and believe you me, the day was not a good one when I raised my concerns about Hicks with Howard in the joint party room," he writes.

But his mother had told him that was one of her proudest moments of his political career, Mr Joyce said.

Mr Joyce also reveals that his mother has recently been diagnosed with cancer. He would now try to "help her as best I can", he said.