The Gillard government will move ahead with a plan to excise the entire Australian mainland from the migration zone, effectively stripping rights from asylum seekers who reach the continent by boat.
The change was recommended in August by the government's expert panel on asylum seekers, chaired by former defence chief Angus Houston.
It is similar to a Howard government plan which was abandoned six years ago in the face of opposition from Liberal moderates.
Currently, only asylum seekers intercepted at sea or at Christmas Island, the Cocos Islands or Ashmore Reef can be sent for processing on Nauru or Papua New Guinea.
Immigration Minister Bowen said that the government was trying to remove the incentive for people to try and make it all the way to Australia.
"We're trying to save people's lives here," he told Sky News.
Mr Bowen said that the government was trying to remove any opportunity for people smugglers to make dangerous promises such as, "I can get you to the mainland, so you won't be sent to Nauru."
"We do need to close down any opportunity for people smugglers to spin," he said.
The legislative change was taken to caucus this morning and was approved but members of the Left faction did raise their concerns.
The Left factional bosses secured from Mr Bowen a commitment to have ongoing discussions about refugee policy.
Although the Left agreed to support the immigration changes long ago, there was still significant discomfort among the faction about policy direction.
''We will continue to have discussions with Bowen about a number of issues,'' said one member of the Left.
This Labor government is now going to try to enact legislation that is so discriminatory and un-Australian that John Howard faced an internal revolt when he tried it in 2006.
Legislation could be introduced as early as this week.
Mr Bowen's office said the changes would not apply to asylum seekers who arrive by air.
It is rare for asylum boats to reach the mainland, but in April a boat carrying 10 Chinese nationals arrived in Darwin, and in 2008 a boat carrying Sri Lankan asylum seekers made it to Shark Bay, in Western Australia.
While Mr Bowen acknowledged that there were not large numbers of people arriving on the Australian mainland by boat, he said the new excision announcement sent a "significant message".
Coalition immigration spokesman Scott Morrison noted the proposal was similar to that put forward by the Howard government, but would not commit the Coalition to supporting the measure.
''When we see the legislation we'll take it through the normal processes,'' he told reporters in Canberra.
''I find it interesting that the Minister has not sought to alert me to this. I don't think that's in the spirit of how we've been dealing with things coming out of the Houston report.''
Asked about the plan today, Opposition Leader Tony Abbott would not say whether the Coalition would support it.
''We'll wait and say exactly what we're going to do when we see the relevant legislation. I haven't seen any legislation,'' he told reporters in Canberra.
''I understand the government had a huge argument in the caucus about this this morning. Let's wait and see what the government comes up with.''
Greens immigration spokeswoman Sarah Hanson-Young said the Greens would oppose the change, describing it as a ''shameful piece of legislation that discriminates against some of the most vulnerable people in our region, based on the way in which they arrive in Australia''.
"The government will say that this is about discouraging people from getting on boats but it is clear that the only way to achieve that is by offering people safer pathways, not by removing people's fundamental right to apply for asylum in Australia,'' Senator Hanson-Young said in a statement.
''Rather than trying to help these vulnerable people, this Labor government is now going to try to enact legislation that is so discriminatory and un-Australian that John Howard faced an internal revolt when he tried it in 2006.
"It is such a bad piece of legislation that even Barnaby Joyce threatened to cross the floor. It was a bad law then and it is a bad law now.''
with Judith Ireland