Chelsea Manning, the controversial whistleblower who leaked nearly 750,000 classified US documents to Wikileaks, could have her Australian visa cancelled ahead of an upcoming speaking tour.

She plans to speak at the Sydney Opera House on the weekend, launching an Australian tour.

But the organiser of the event, Think Inc, claims it has received a letter from the Australian government warning her visa may be refused under Section 501 of the Migration Act.

life after prison & solitary confinement is harder than i ever imagined, but i'm trying my best 💖 excited to be visiting Australia & New Zealand next month 🌏✈️🌈💕 @theprojecttv pic.twitter.com/35wvFOJJj2 — Chelsea E. Manning (@xychelsea) August 6, 2018

The section gives both Home Affairs minister Peter Dutton and new immigration minister David Coleman the power to cancel her visa on “character grounds”.

Following the letter, Think Inc has called on the government to allow Ms Manning to come to Australia - presenting letters of support for the former American soldier.

"We have been vigorously advocating for permission for Ms Manning to enter Australia - we are of the view that she poses no threat to members of the Australian community," the appeal reads.

"Think Inc. believes Ms Manning is entitled to freedom of expression and political opinion which are foundations of a free and democratic society and fundamental human rights."

AAP

Think Inc.'s director Suzi Jamil said Ms Manning offered "formidable ideas and an insightful perspective".

"We hope that the Minister for Home Affairs and his Department will not stand in the way of the Australian people hearing Ms Manning's story," she said.

"We intend to pursue all legal avenues and hope they will allow the Australian public to hear about vital issues around data privacy, artificial intelligence and transgender rights. As this may be a stressful time for Ms Manning, I hope this issue can be resolved in a positive manner with no further unnecessary complications."

The petition has been echoed by Peter Greste, the well-known Australian journalist who spent more than a year imprisoned in Egypt for his reporting, was scheduled to interview Ms Manning at the weekend.

0:00 00:00 / 00:00 Share Share on Twitter

Share on Facebook

Mr Greste told SBS News he was “incredibly disappointed” to learn a visa refusal was on the cards, but said he still hoped for a last-minute approval.

“There’s no denying that Chelsea was responsible for a pretty extraordinary leak of classified information and she’s been convicted of that,” Mr Greste said.

“But the first question ought to be whether she poses a threat to Australia, and the answer to that must surely be no.”

0:00 00:00 / 00:00 Share Share on Twitter

Share on Facebook

He said there was no risk of Ms Manning overstaying her visa or leaking Australian state secrets.

“Unless there is a clear, demonstrable risk to Australia we ought to be doing all we can to bring her in and hear what she’s got to say. I think anything less than that is undermining democracy,” he said.

But Mr Dutton’s office and the department both told SBS News they would not comment on individual cases.

“A person can fail the character test for a number of reasons, including but not limited to where a non-citizen has a substantial criminal record or where their conduct represents a risk to the Australian community,” the department wrote in a statement.

0:00 00:00 / 00:00 Share Share on Twitter

Share on Facebook

"All non-citizens entering Australia must meet the character requirements set out in the Migration Act 1958 (the Act)".

Chelsea Manning threatened with visa denial ahead of Australian tour. I was due to interview her at the Opera House. She has a lot to say, and we have nothing to fear. https://t.co/UfAH7GJxYb… via @smh — Peter Greste (@PeterGreste) August 29, 2018

Ms Manning's previous conviction in the United States could threaten her visas to both Australia and New Zealand.

Her 35-year sentence was commuted, not pardoned, by former president Barack Obama. Therefore, she still has a standing conviction and will have to request special dispensation to be granted a visa to visit both countries.

Section 501 of the Migration Act gives the minister the power to refuse visas on "character grounds". The power has previously been used to ban speakers who advocate anti-vaccination theories or violence against women.

Labor frontbencher Penny Wong said it was "up to the government to explain why they are doing this".

Senator Wong told ABC Radio the possible refusal "seems pretty inconsistent", following this week's revelations about how Home Affairs minister Peter Dutton intervened to spare an au pair from deportation.

AAP

Think Inc has asked its supporters to lobby the immigration minister.

"We are looking for support from relevant national bodies or individuals, especially politicians who can support Chelsea's entry into Australia," Ms Jamil said.

"We are seeking letters of support to send to the Minister for Immigration in order for him to reconsider his decision."

It comes as opposition politicians in New Zealand call for Manning to be banned from entering that country.

The centre-right National Party on Tuesday called for the government to decline that request, saying Ms Manning was a "felon".

"Chelsea Manning used a position of responsibility and authority to steal hundreds of thousands of documents that may well have put American lives at risk," party immigration spokesperson and former minister Michael Woodhouse told Radio New Zealand.

"This is not a question of free speech. (Ms Manning) is free absolutely to say whatever she wants but she's not free to travel wherever she wants. Other countries have already denied her entry."

AAP

It was inappropriate for Ms Manning to make money by talking about her crimes, Mr Woodhouse said.

But lobby group the Free Speech Coalition swiftly condemned the calls to bar Ms Manning.

"There are other examples of previously convicted criminals that have been allowed entry into New Zealand. Nelson Mandela was allowed entrance in 1995," spokesman Chris Trotter said.

"The subject of our allies' wartime conduct is a matter of great public importance."

The Green Party has also come to Ms Manning's defence.

AAP

New Zealand's immigration department says it's received an application, which will now be looked at by senior officials in the first instance, with a right to appeal to the minister in charge.

Associate Immigration Minister Kris Faafoi's office said he would not comment on individual cases.

- with AAP