Key crossbench MP Tony Crook still undecided on Labor's offshore processing amendments

WA Nationals MP Tony Crook says all offshore asylum-seeker processing could face legal challenge under current migration laws.

WA Nationals MP Tony Crook says all offshore asylum-seeker processing - including on Nauru - could face legal challenge under current migration laws.

But the key crossbencher says he yet to decide if he will support Julia Gillard's Migration Act amendments to put offshore processing beyond doubt, or deal the government an historic defeat in the House of Representatives.

Mr Crook said he didn't support the Malaysian people swap, but he backed offshore processing and believed his electorate wanted a strong border protection policy.

He said he believed the Coalition's preferred offshore processing option of Nauru could be challenged following the High Court's August 31 ruling that the government's Malaysian people swap was unlawful.

“Having considered what happened over the Malaysia deal I wouldn't be at all surprised of a legal challenge of anything that comes up now and that is obviously a concern,” Mr Crook said.

He said he would meet separately with Opposition Leader Tony Abbott and Labor's Anthony Albanese to discuss the government's proposed migration law changes.

Mr Crook signalled he would not make a decision on his support for the amendments until closer to Thursday's expected vote on the proposed changes.

He said he hoped to meet with the Prime Minister before securing his support one way or the other.

“I am weighing up all the information I can get on this argument and I will make my decision in due course,” he said.

Mr Crook's fellow crossbencher Rob Oakeshott also said his support for the government's migration amendments was not yet locked in.

Mr Oakeshott introduced his own amendments to the government's changes which called for a regional approach to asylum-seeker management to be codified into Australian law.

He said if the measure did not pass through the House of Representatives his support for the government's changes could not be guaranteed.

“It is a bit of a card game going on. What I am trying to do is elevate the Bali Process where there is regional cooperation and if the Coalition were to knock that out well that would be pretty churlish, but let's see how it plays out through the proper parliamentary processes.

If Labor's amendments are voted down it would leave the government with the option of onshore-only processing, which experts have warned would encourage more boat arrivals.

It would also be the first time in 80 years that any federal government would have lost a lower house vote.