While the crossbench remains concerned about legislation that will strip dual nationals of their citizenship if they are believed to be fighting with terrorist organisations, Labor is prepared to pass the legislation as early as today.

The Australian Citizenship Amendment (Allegiance to Australia) Bill would allow the government to strip dual nationals of their Australian citizenship if they have been convicted of a terrorist offence, if they have gone overseas to collaborate with a terrorist organisation, or if they have fled Australia after committing a terrorist act, thereby preventing them from returning.

The government made several amendments to the legislation in response to the Joint Standing Committee on Intelligence and Security’s report on the legislation, including limiting the retrospective aspect of the legislation to only strip the Australian citizenship of people convicted of terrorism offences carrying penalties of 10 years’ jail in the past 10 years. At the last minute the government added a “technical amendment” to the legislation last week, on a second round of advice from Solicitor-General Justin Gleeson.

The opposition and the crossbench were briefed on these technical changes, but the government has not explained in full what the changes are. It is believed that the two letters from the Solicitor-General relating to the legislation were giving advice to the government on how to avoid potential constitutional challenges over the executive having the power to strip citizenship. The government has refused to release the letters to the public — or to opposition and crossbench MPs and senators — outside of a supplementary explanatory memorandum tabled in the Senate yesterday.

Attorney-General George Brandis explained the second change to the legislation was because Gleeson believed that if the immigration minister had to consider whether to spare a person from an automatic loss of citizenship after the person served time for a terrorism-related crime, that would potentially be a breach the constitution. The minister would be “the effective decision maker”, and this could be characterised as an exercise of judicial power.

Despite not having access to Gleeson’s advice, Labor is happy to take the government at its word, with shadow attorney-general Mark Dreyfus this morning on the ABC criticising the government for not releasing the advice, but saying Labor would back the legislation regardless:

“We’ve been forced to rely on the government’s assurances that the bill, as amended, is constitutional … The government has refused to provide the two pieces of legal advice the Solicitor-General has given. We do have no option but to accept the written assurances from the Attorney-General that the Solicitor General has advised this bill — in fairly qualified language I must say — will pass muster in the High Court.”

In the Senate yesterday, Labor Senator Joe Ludwig said that although Labor would support the legislation, it would be up to the government to defend and explain the laws if they were challenged in court, and denied Labor was rolling over again on national security legislation:

“Make no mistake, though; this is not a blank cheque that Labor is offering the Coalition. On the issue of national security, Labor and Mr Bill Shorten have worked constructively with the government. There is nothing more important than keeping the Australian people safe, and this issue must be kept above politics.”

The crossbench is offering more of an opposition to the legislation than Labor, however, pushing debate on the legislation out to today before it is voted on. Independent Senator Nick Xenophon said terrorists left overseas rather than being brought to Australia to face punishment could ultimately attempt to work out how to target Australians abroad:

“My concern is: are we taking the easy way out by simply revoking their citizenship and allowing them to free-range in the rest of the world with their murderous intent? And that murderous intent may include targeting Australian citizens who are either holidaying or living overseas.”

In contrast with the foreign fighters legislation, which would prevent people leaving Australia to participate in terrorist acts, the current legislation says once that person is overseas, that person is not welcome back in Australia, Xenophon said:

“If we have a person with evil, murderous terrorist intent and if we can in any way drag them back to Australia and lock them up for a very lengthy period and throw away the key if need be, I would have thought that would make it safer rather than these people free-ranging.”

Greens leader Richard Di Natale said the legislation was a “hangover” from the Abbott government and that Prime Minister Malcolm Turnbull had initially resisted it:

“It is our view that once somebody is convicted of having committed a serious crime, and these are very serious crimes, then the best place, the safest place, is for those people to be in custody here in Australia.”

Liberal Democrat Senator David Leyonhjelm said the legislation was a “violation of the doctrine of separation of powers”, and criticised Labor and the government for adding 14 new pages to the legislation the day before and expecting the crossbench to vote on it.

Leyonhjelm and Xenophon have both said they intend to table amendments to the legislation today. Independent Senator Jacqui Lambie asked Brandis if he would resign if the legislation was challenged in the High Court. Brandis said he would not pre-empt any potential challenges in the High Court: “Nobody should make hard and fast predictions about what may be decided by the High Court, and I do not intend to do so.”

It is expected the legislation will pass this sitting week, the last sitting week of the year.