Manning's tour was due to start in Sydney on Sunday, but on Thursday event organizer Think Inc. said it had received a notice of intention from the Australian government to deny Manning entry.
Think Inc, the Australian organiser of Manning's tour, has written to supporters asking them to lobby new Immigration Minister David Coleman, Australian media has reported.
"All non-citizens entering Australia must meet the character requirements set out in the Migration Act 1958 (the Act)".
"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.
"The request includes more than 10 letters of support from individuals and organisations who stand with Ms Manning and support her entry to Australia".
"But the first question ought to be whether she poses a threat to Australia, and the answer to that must surely be no".
Chelsea Manning, formerly Private Bradley Manning, was incarcerated and tortured in military prisons and sentenced to 35 years' imprisonment under the Obama administration. Her sentence was commuted by former US President Barack Obama.
"Ms Manning has many formidable ideas and an insightful perspective which we are hoping to bring to the forefront of Australian dialogue".
The former U.S. army intelligence analyst has a scheduled speaking tour in Australia and New Zealand in September, and it appears she wouldn't be allowed to set foot in either.
Opposition politicians have also called for Ms Manning to be banned from entering New Zealand.
Prime Minister Scott Morrison said the decision was for Mr Coleman, who was sworn in on Tuesday. "This decision must be reversed and Chelsea Manning must be allowed to continue with her speaking tour so Australians have an opportunity to engage in discussion of human rights issues".
"She won't incite violence or hatred in a way that other people who have been allowed into this country have done in the past".
Ms Jamil said Ms Manning was "so far from a risk to the Australian public". "If [the Coalition] consider themselves proponents of free speech they should let her in". "Nelson Mandela was allowed entrance in 1995", spokesman Chris Trotter said.
Section 501 is the same section of the Act used to deport hundreds of New Zealanders with criminal convictions on character grounds.
Woodhouse said if Manning's application had come across his desk as immigration minister he would have declined it.