A new One Nation push to permanently block former ISIS fighters and their supporters from returning to Australia is “unlikely to be constitutional”, a national security law expert has warned.

Pauline Hanson will introduce legislation when Parliament returns on Tuesday aimed at strengthening powers to cancel or refuse passports and tightening bail laws for people facing terrorism charges.

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But the proposal is already facing serious questions over whether it could survive a challenge in the High Court.

Dr Danielle Ireland-Piper, Associate Professor at the ANU National Security College, told Sunrise there were significant constitutional and international law hurdles in Hanson’s way.

“It’s unlikely to be constitutional or permissible at international law to permanently ban a citizen from returning to their own country,” Ireland-Piper said.

Pauline Hanson’s plan to block ISIS fighters from returning to Australia could face a major legal challenge. Credit: Sunrise

She said one of the key constitutional problems was Australia’s seperation of powers, which limits Parliament’s ability to effectively impose punishment that should be determined by a court.

“One of the reasons Australia is a relatively peaceful country is that we have rule of law. Our constitution is the overriding document, the blueprint of the nation,” she said.

Ireland-Piper said this created technical difficulties if Parliament attempted to dictate the outcome of a case to the courts.

The proposal could also clash with Australia’s obligations under international law, particularly when Australian citizens are accused of committing crimes overseas.

“In some ways there’s a moral responsibility on Australia to bring people back here to prosecute if they have engaged in criminal conduct,” she said.

If Hanson’s bill attracts enough support to pass Parliament, it will likely be tested in the High Court.

Labor has also raised concerns that refusing to accept Australian citizens could have wider consequences for the country’s ability to deport foreign criminals and co-operate with other nations.

Ireland-Piper said countries relied on reciprocal arrangements when dealing with deportations, extraditions and other cross-border criminal matters.

“If we’re not willing to accept our citizens when they return, that could compromise our agreements with other countries around deportation and extradition and other types of crime cooperation,” Ireland-Piper said.

“There’s a number of issues here, it’s very unlikely that you can permanetly prohibit a citizen from returning,” she said.