Turnbull faces backbench revolt

Federal Opposition Leader Malcolm Turnbull's leadership was further undermined on Wednesday amid the second backbench revolt in a week.

Liberal backbenchers Petro Georgiou, Judi Moylan, Danna Vale and Russell Broadbent plan to cross the floor to vote with the government on its legislation abolishing the practice of billing asylum seekers for their mandatory detention.

Mr Georgiou, who will retire at the next election, fought back tears as he told parliament on Wednesday that no advanced society should charge innocent people for the cost of their incarceration.

"Do we make major drug dealers, serial pedophiles, sadistic murderers or multiple rapists pay the costs of their incarceration?" he said.

"The answer is that we do not."

The dissent comes after four coalition MPs on Monday night defied their leader to vote against the government's 70 per cent alcopops tax hike. Nationals leader in the Senate Barnaby Joyce says he won't turn up for the upper house vote, and colleague Fiona Nash has also said she won't support the bill.

Coalition MPs have been directed to vote against the government bill that aims to abolish the policy of charging asylum seekers for their detention.

Detainees can face debts totalling more than $45,000 for each year of incarceration.

The legislation also waives existing debts for current and former detainees, but it won't refund any debts already paid.

Ms Moylan also fired a salvo at her coalition colleagues who oppose the bill.

"I have to say that I am extremely disappointed that, once again, politics are played at the expense of some of the world's most vulnerable people," she said.

"I don't think these are the kind of people that we need to further punish.

"I think they've been punished enough."

Opposition immigration spokeswoman Sharman Stone said that since the Labor government changed its immigration policy in August, 22 illegal boats had been intercepted carrying more than 900 asylum seekers, including a vessel off Ashmore Reef that was discovered on Tuesday.

"There is no doubt that announcing to the region that the Rudd Labor regime is abolishing the 17-year-old policy ... will bring great joy to people smugglers who are once again very active in our waters," she said.

"We can't support further watering down of border protection policy and the integrity of our humanitarian refugee program."

Queensland Liberal Stuart Robert quoted former prime minister John Howard in his speech, saying: "We should continue to decide who comes to this country and the circumstances in which they come".

Debate on the Migration Amendment (Abolishing Detention Debt) Bill 2009 was adjourned.