The Coalition is not saying whether it will support the government's plan to excise the entire continent of Australia from the migration zone.
The Labor caucus on Tuesday approved laws to introduce the change, which would see rights stripped away from asylum seekers who arrive by boat.
By expanding the migration excise zone to the mainland, the government would be reviving a plan dumped by the Howard government following a backbench revolt led by Liberal moderates.
Opposition immigration spokesman Scott Morrison said the coalition would have to see the bill before it decided whether to support it.
"When we see that bill we will take it through our normal procedures as you could expect us to do," he told reporters in Canberra on Tuesday. Coalition MPs would be free to have their opinions heard on the matter, he said.
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"There are a number of members on our side of the parliament who have held consistent views on this issue," Mr Morrison said.
"I would expect any decision they took to act consistently with their long-held principles."
Mr Morrison accused Labor of hypocrisy for deciding to introduce the policy after opposing it while in opposition.
"I am surprised that they have rolled over like little lambs," he said. "While they were lambs in the caucus today, in the parliament six years ago and on these matters more generally they have roared, and roared and roared at the coalition."
Under existing migration laws, only asylum seekers intercepted at sea or at Christmas Island, the Cocos Islands or Ashmore Reef can be sent for processing at Nauru or Papua New Guinea's Manus Island.
