Chelsea Manning has been barred from visiting Australia for a speaking tour after failing a character test, her event organiser has said.
Ms Manning, who served seven years of a 35-year sentence for passing classified information to WikiLeaks, had been due at the first of a series of public talks on Sunday.
But event organiser Think Inc said it had received a notice of intention from Canberra to deny Ms Manning entry.
In the letter, obtained by the Australian Broadcasting Corporation, the whistleblower was told her “substantial criminal record” made her ineligible for entry.
Australia’s Department of Home Affairs refused to comment on her case but said all non-citizens entering Australia must meet character requirements set out in the Migration Act.
The reasons a person might fail the character test include a criminal record or a determination they might pose a danger to the community.
Amnesty International said the ban would “send a chilling message that freedom of speech is not valued” in Australia.
“Denying her entry based on a past criminal conviction would be a restriction on her right to freedom of expression and would hamper her legitimate human rights work,” Claire Mallinson, director of Amnesty International Australia said.
“Chelsea Manning should not continue to face penalties after the time she served in jail and the commutation of her sentence by presidential order.”
The country’s new prime minister, Scott Morrison, said a final decision would be taken by the new immigration minister, David Coleman, who was sworn in on Tuesday.
Australia’s visa system allows applicants denied entry a right to appeal, however precedent suggests Ms Manning will struggle to overturn the decision.
In 2014, a controversial US “pick-up artist” was forced to end his Australia tour early after having his visa revoked.
A year later, Chris Brown was denied entry for his music tour on character grounds.
However a lawyer who has represented WikiLeaks founder Julian Assange said people with criminal records have been allowed into Australia in the past.
Greg Barns said no one would seriously suggest the transgender activist was a risk to the Australian community.
Ms Manning also faces a ban in New Zealand, where she has two speaking events in September.
Immigration New Zealand, the government agency that handles visa requests, will make a decision by Friday on whether to grant her a “special direction” visa.
Without one, Ms Manning does not qualify for entry because she has a criminal conviction within the past 10 years for which she had a sentence exceeding one year, according to the country’s visa rules.
New Zealand’s centre-right opposition has urged the government to decline her visa request.
Ms Manning was convicted in 2013 of 20 charges, including six Espionage Act violations, theft and computer fraud, but was acquitted of the most serious charge of aiding the enemy.