Tony Abbott appears likely to win support from the Labor opposition as well as his own cabinet dissidents for a narrowly defined law automatically stripping citizenship from Australian foreign fighters who hold dual nationality, despite warnings from constitutional lawyers that it may be struck down by the high court.



But it remains unclear how the prime minister intends to make good a promise to strip citizenship from dual nationals still living within Australia without them first being convicted in a court.

The government’s “discussion paper” announcing the controversial citizenship changes stated that the “government intends to modernise the Australian Citizenship Act to enable the minister for immigration and border protection to take action in the national interest to revoke the Australian citizenship of dual citizens who engage in terrorism that betrays their allegiance to Australia. These powers would be used against dual citizens who join or support listed terrorist groups such as Daesh, or engage in terrorist acts alone. They would apply to dual citizens who engage in terrorist activities here in Australia or on foreign soil, including that of our friends and allies.”

But several ministers raised objections in a leaked cabinet dispute over the policy and the Labor opposition voiced deep concerns that allowing the immigration minister, Peter Dutton, discretion to revoke citizenship ran counter to constitutional provisions for the separation of powers and would be struck down by the high court.

Tony Abbott says Australia will strip the citizenship of dual nationals. Link to video

The government has modified the plan – proposing to amend section 35 of the citizenship act which automatically revokes the citizenship an Australian dual citizen who “serves the armed forces of a country at war with Australia” to include those who take up arms with a declared terrorist group. This would not involve ministerial discretion, and if anyone losing their citizenship in this way tried to re-enter Australia or reapply for a passport a court could review all the facts behind the revocation as well as the process by which the decision was made. There is no precedent for making decisions under section 35 because it has never been used.

The communications minister, Malcolm Turnbull – one of those who fought the original plan within cabinet – has publicly argued in favour of the revised proposal.

And Labor also appears open to it: the shadow attorney general, Mark Dreyfus, told Guardian Australia the opposition would wait to see the legislation on Tuesday but added: “Labor has said all along that we support updating section 35.

“My key concern has been having a ministerial discretion based on a whim without proper involvement of the courts, which is what the discussion paper and Peter Dutton have been proposing. If the speculation is right and this proposal has been dropped then Labor has been justified in raising its concern.”

The Labor leader, Bill Shorten, said the prime minister appeared to be preparing for a “significant backdown”.

“He said he wanted no judicial involvement, now it appears he’s been smacked down by wiser heads around the cabinet table”

But Shorten said he was still worried the laws would be struck down by the high court.

“If these laws get struck down by the high court, I’m worried the gate will be opened for these people to come back to Australia solely because of Tony Abbott’s ineptness and determination to ignore legal advice. No one wants dual citizens fighting for Daesh back in Australia, no one. Any dual citizen taking arms against Australia should be stripped of their citizenship,” he said.

“I am concerned that the Prime Minister’s increasingly extreme, hysterical language is making people feel more unsafe and his repeated delays on the new laws are having serious consequences.”

Earlier on Sunday, Shorten told ABC Insiders: “The Labor party does not support and we are deadly against dual citizens who are terrorists keeping their citizenship.

“Let me repeat that. Under the current citizenship act, section 35, if an Australian dual citizen takes up arms against Australia in service of an enemy country they can lose their citizenship. I support the principle of extending this to terrorist organisations who might not be foreign countries but they have the same taking up arms against Australia.”

Last week Abbott accused Labor of “rolling out the red carpet” for foreign fighters after Dreyfus said a foreign fighter would have to be brought back to Australia to secure a conviction. Asked about the comments, Abbott said they showed a “clear difference” between government and opposition.

“The government wants to keep them out, we want to keep terrorists out of our country; the opposition – the Labor party – wants to bring them back.

“It seems that the opposition wants to bring them home; no doubt roll out the red carpet for them like it rolled out the red carpet for people smugglers when it was in government.”

Legally the new plan relies on the assessment that the decision to revoke citizenship becomes effective when the foreign fighter seeks to be considered a citizen – upon returning to the country or asking for a passport, for example, and at that point it would be assessed and determined by a court.

But leading constitutional lawyers remain doubtful.

Prof George Williams from the University of New South Wales told Guardian Australia that to be constitutional the revocation would “have to look like an administrative decision and not a punishment … because a politician cannot declare you guilty of an offence and judicial review after the decision does not cure that constitutional problem.”

Williams said he believed there would remain “significant risk the law would breach the separation of powers”.

The prime minister has conceded there is an element of constitutional “risk” in the plan while saying the government has received advice saying it is likely to be valid.

But it remains unclear how the government could overcome the constitutional problems of revoking the citizenship of someone still in Australia who has not been convicted in the courts.